I think there's just some concern over competition with people doing similar things. And that's understandable, but I'm not sure the comments against a conversion display favor a full-blown kit (more on that below). I think there's probably much more of a market [in the US anyway] for Bally conversion displays than there would be for Zaccaria. And maybe price is a factor there too as it looks like the conversion Zaccaria display kits are about $27 USD at their cheapest, whereas a full-blown kit is $48. Perhaps if the conversion displays were $20, then compared to the other option of $48 full-blown displays they would get more attention.
Anyway, I'll address some of the other thoughts..
1. Cheaper Assembled Displays. If there's $30ea assembled displays somewhere as mentioned, I'd love to see a link. But this would make any of the current full-blown display kits out there not worth selling too.
2. Cost. From what I've seen, even at $20 per conversion display -- that's still cheaper than anything else out there. This makes up for lacking a few features I think. And it would very likely be less than $20 if a full set was purchased (ie. $90-95 for a set of 5x which puts the per display cost at about $18-19ea). I did have thoughts of offering these several different ways too.. if people wanted to source components themselves. I figure people wouldn't mind having options both ways though, just like I'm sure these kits won't be for *everyone* as some people would rather shiny new boards for the entire display or something already assembled & completely plug-and-play.
3. Build time. Obviously it depends on experience and tools, but I don't see labor/time involved in a conversion kit being any more than with a full-blown kit that would likely take 45-60min build time per display. I actually think a conversion kit could go pretty fast after someone did a few of them.. probably 20-30 minutes each. Maybe closer to 1hr if you wanted to completely remove components instead of soldering many of the resistors in parallel on the back of the board.
4. Aesthetics. The display would look as-nice as other kits out there when installed in a machine. Most people aren't looking at the component boards and the component board would still look nice enough as well. On the back, worst case there's a jumper wire and some resistors soldered in parallel. The drawback as with most DIY displays is no commas (or custom digits). Plenty of people seem fine with no commas though if the price is right.
5. No Dimming / PWM. Yeah, that's a feature this wouldn't have. But if someone wants to adjust the brightness they could swap out resistors on the segments easy enough.. or even use 1pos SIP sockets on those resistors for the first display and swap resistors around until they found what brightness worked. I'm pretty sure even on displays that have a dimmer, most people are just going to set the level initially when installed & it's never going to be touched again. It's a nice "feature" but to me kind of unnecessary after the initial install. These are DIY, so it's easy enough for someone to swap out resistor values if they want to achieve a different brightness.. and once you find what works you could use that as the model for other displays being built.
6. Power Consumption. I've seen mentioned *over and over* how led displays could tax the 3A 5v regulator. Instead of guessing what load was being added, I did both analysis on the machine load without led displays & then again with a few aftermarket led displays added. Only one of the aftermarket displays hit the regulator hard (about 220-230mA additional load per display added). I used these tests while working with this conversion display idea & it looks like they'll be about 80-95mA measurable load per display in the worst-case of all 8s held on the display. I need to verify that again, but that's considerably less than 220mA from the "less efficient" aftermarket display that has been sold & used in many games. None of this is an argument against adding power saving components (ie. PWM, regulator) on full led display kits.. but there are plenty without them and the machines can support it because of multiplexing & the head-room even on a 3A 5v regulator. At least from what I have seen with the load, there appears to be plenty of head-room.
7. Savings/Economics. People seem okay with saving $35-40 by buying a set of displays as a kit over assembled displays that have custom digits. I'm a bit surprised by that, but everyone likes something different & saving money is still saving money if you don't mind putting in the time. Saving near $100 by converting old displays (while also having the positive benefit of helping the environment) should then be all the more appealing.
I hope that addresses some of the things mentioned. It really isn't a big deal even if there wasn't interest in this any more than for my own use, but it's looking like there's enough interest to justify having some of these made up and not having to worry too much about getting "stuck" with materials.
For me, $150 for kits is too close to $185-195 for an assembled display that's plug-and-play and uses custom digits, not enough to motivate me to go the kit route. I'd rather save the time and buy assembled. A $90-95 conversion display set though.. if the labor isn't too bad and the end result is nice -- now that has my interest. And the reason why is that many of these older Bally/Stern games are sub-$1000 machines. It's easier spending $200 for a new display on the later System 11, WPC, etc games when the games are $1500-2500+. But putting an additional $200 into a $600-800 Bally/Stern, that's too high a percentage I think. That doesn't really make sense to me, unless it's a long-term keeper or you only have a few machines. But a way to upgrade to LED displays for $90-95 per machine.. now you've got my attention. Now the numbers work out (with respect to machine value versus display cost).