I originally wanted to add the upper sling back to the game, considering that it was in the original design and would make the game more interesting. But after looking into it I read that the sling had a tendancy to send the ball down the left outlane, so it was removed. And even though the solenoid wiring still exists in the harness, I found out while going through the source code that the routine had been completely deleted. Simply wiring up the solenoid would not make it work.
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I revisited the deleted sling after I had updated the code with new features. I could've easily added the routine back in, but again, the thought of it sending the ball to the outlane kept me from doing it. Freefall is frustrating enough as it is, it doesn't need any help in that department from the upper sling. The game is designed to be a drainer.
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I added the flipper after giving the left target bank some new rules, and it can actually be both a blessing and a curse. There is some strategy to it. One thing I had hoped for was to be able to hit the left lane stand up target. Unfortunately, it's like trying to make the riptide shot on Seawitch from the upper flipper. I'm going to see if curving the ball guide will make a difference.

But to answer your poll question, YES, the third flipper does improve gameplay. With the stock rules and the left target bank not being worth much, the main benefit is deflecting the ball from going SDTM after a bounce off the right rubber. But with the enhanced rules it entices players to shoot the left target bank.

I didn’t get it either. It’s essentially an EM with a novelty multiball added. The new rules spread out the shots instead of the center bank being a one-trick pony.

New rules include:
Ball in Freefall kicker spots a Sky Divers letter (3-ball setting in stock code already does this, but it’s not documented)
Left target bank spots a letter
Left target bank in sequence advances altitude value by 100k, up to max 125k and blinks 100 lamp in left lane
Left standup increases altitude by 5k
Hitting left lane standup when 100 lamp is blinking spots all letters (carries over ball to ball until collected)

Multiball rules:
No ball relock during multiball
Letters blink during multiball when collected, collecting blinking letters scores 5x value and increases altitude value by 5k, up to max 125k
If 125k altitude is reached during multiball, left lane lamps will animate for jackpot
Jackpot scores 10x altitude = 1.25 million! (altitude will reset for next jackpot buildup)

All of the original rules are still in place with the exception of multiball relocking.