is the 7750 that unreliable?
Relatively it is, though the quality has improved a little in the recent batches,but compared with other rep movements like the A2836/2824, and A7750 sec@9, the movement needs some work to be reliable, and even then the design remains questionable and the chrono function is precarious at best. The design to transfer the running seconds from 9 to 12, while innovative, creates additional friction points in the top plate and this can lead to sporadic stoppage if any point in the transfer gear train is not well-lubricated/well-aligned. The movement design is not changed after an overhaul, and often, members do not understand that a movement service for this particular movement does not turn a problematic design into a bulletproof movement where they can start spamming the chrono all day and still expect longevity out of it. It is still wise to leave the chrono well alone in the A7750 sec@12 movement, serviced or otherwise.
So in this regard, the movement is not reliable if you take in the limited reliability of the chrono function. If it is only used as a time keeping device, the reliability is still not par with the A2824 or A2836. So I will still classify the A7750 sec@12 movement as challenging, no matter which way you look at it. There has been many instances of the movement working fine for x weeks or months and then stopping one fine day due to various causes. There is enough documented evidence to suggest that this, along with the 7750 sec@6 or 3, forms the bottom tier in terms of movement reliability in this hobby.