I've had an inordinate number of failures with button gauges, both personally and at a former employer.
Functionally, the inability to clock them is annoying. Their resolution may be fine for something like a rebreather bottle where you don't really care about accurate information, but for actually using it when gas volume is important, they are iffy at best.
Quality wise, I have found them far less accurate than normal SPG's. The worst offender was approximately 500 PSI off, but generally between 100-250 psi off. This is all based off of digital gauges on a full Bauer fill station. If you need to know how much gas you have, it's no good.
They are also more prone to failure. Stuck needles are a reality and far more common than a normal SPG in my experience. I have had 2 seize completely, rendering them absolutely useless. I've also found them far more prone to leakage.
My sample size is around 40 button gauges of varying brands. A handful, 5-10 at best, were both accurate and reliable. The rest showed varying levels of inaccuracy, varying levels of reliability, and getting them to clock was a crapshoot. Perhaps 20% of them were correctly oriented when tightened.
Shearwater has seemed to have the connection reliability thing licked pretty darn well, compared to the competition anyway. Why intentionally introduce an unreliable failure point into a system, that may or may not even be accurate or readable, especially when it's more unreliable than the system it's designed to back up. Carrying a real SPG is a far more worthwhile backup, for the off chance the transmitter chokes.
Anyway, that's why they're trash IMO.
