The benchmark for SPG's in technical diving is the Italian made Termo Industria "Tech Gauge" (aka "brass & glass") model in two sizes with a dial that has been branded with logos of virtually every technical diving equipment supplier worldwide. Dive Gear Express sells it too, as our "DGX Premium SPG" with an uncluttered dial that does not have our logo on it. Termo specifications for their gauges only reference the European Union recreational EN250 standard, which essentially means all their gauges are officially rated by the manufacturer to the {164 fsw | 50 msw} depth of the standard. Regardless, technical divers have been taking the Termo brass & glass SPG to depths far beyond {330 fsw | 100 msw} without issue, for decades.
Termo Industria also makes a compact SPG model they call the "2K" and we sell it as our "DGX Thin SPG". The Thin SPG has a polycarbonate face cover held in place with a large O-ring seal. The thin gauge has an issue with depths significantly below {164 fsw | 50 msw}; it doesn't flood but you can't trust the indication either. What happens is water pressure causes the plastic face cover to depress slightly into the cavity of the gauge eventually touching and holding the needle against the dial so that it cannot move. When that is happening, the gauge reading as indicated by the needle is unreliable. Once you ascend, the cover returns to normal and the needle returns to normal indication as well. We don't recommend our "Thin SPG" for use significantly below {164 fsw | 50 msw}.