The 89 and 906 "flashers" are not only big and bright, but on pinball machines are typically run at higher than their continuous rated voltage of 12V. That means that if they were on continuously they would overheat and burn out fairly quickly. So they are used for only short term pulsed operation as "flashers" -- they are flashers by pinball game design convention rather than by the inherent characteristics of the bulbs.
The fact that the 89 and 906 bulbs in pinball applications are generally run at higher than rated voltages causes issues for at least one LED replacement bulbs maker -- bcspinball -- and has a voltage/current limiter mod for the flasher circuits (at least for DE games). Other makers like Ablaze seem to have designed their LEDs to handle the higher voltages without issue.
And the fact that pinball machines run their 89 and 906 bulbs at greater than 12V *might* mean that there are problems adapting automative LEDs designed for 12V to pinball applications, even if the base fittings are compatible. Safer to stick ith the bulbs specifically designed for pinball machines, I suspect.