NOT a certified tech, but I have researched the heck out of these things. If you are interested, here's my guesses:
1 - a lot of agencies appear to be offloading their stuff lately. I would be careful diving prior-service stuff.
2 - it is about impossible to determine what is what. An OTS visor will fit in an Interspiro mask frame, no problem. This doesn't make it an OTS item.
3 - frame colors only help a little. They can sort of tell you what the material is (gray - usually natural rubber.)
4 - The older units have the valve 'dogbone' on the wearers right cheek, and you have to remove the nose part to twist the valve to remove it. Newer units have the dogbone on the opposite side (wearers' left), and have an oval aperture that snaps into place on the mask frame. You flip a flipper inside the mask to release the valve if I remember correctly.
5 - the tiny switch at the base of the bulb (valve body) is for what used to be called positive pressure. I am blanking on what the scuba world calls it, but that switch allows the wearer to go from positively pressurized (almost like free flow), to demand only. OSHA removed that switch from SCBA a long time ago. I have not seen a pricing differential between the two, making one more valuable than the other.
6 - I have been following pricing for about a year now. Like I said, other places are dumping these units, driving prices down. They use a proprietary air fitting, so for people to use them they either need Interspiro hoses, or a $90 USD adapter.
On the plus side, most of the parts and consumables are still available. And, they dive pretty well from all accounts. If yours had the accessory mounts, they might actually be worth some cash, as those seem to be fairly pricey even today for some reason.
Message me if you have more questions, and I'll try to help.
