There are basically 2 "standards" on the market.
The Omniswivel CEJN fittings are the standard for FFM's. Nipple on the regulator, body on the hose and they're essentially a giant inflator hose like on your BC. They have been the standard in that world for many years because the nipple is so small. They were the standard in CCR's for a while until they almost killed a couple divers because they made a slight change and they were not compatible in one direction anymore *can't remember if it was new body didn't fit old nipple or vice versa, but doesn't matter*.
When that happened, the CCR world went to Swagelok QC6 and that is essentially the standard for the CCR and cave world. QC6 is advantageous because they are double end shutoff, but are much larger and heavier so you need an intermediate hose between them and your mouth.
So the Omniswivel is the standard in public safety, Swagelok QC6 is the standard in the cave community.
The DiveGearExpress ones for like $30 are perfectly fine though and if you think you need them, then I would probably start there since you'll be out $35 instead of $100 for the Omniswivel.
Now, on my actual opinion.
When I dive FFM, my FFM has an omniswivel QC on the mouthpiece that connects it to the switch block, and the switch block has QC6's on it to connect to my tanks *because I have QC6 on all of my regulators for CCR* and for some of the diving that I do it is required that I have a switch block. I always carry a spare half mask, but I don't intend on using the Omniswivel as a QD underwater. If that second stage fails for whatever reason then I switch to the second stage around my neck and abort the dive. Fix it at the surface. If your FFM fails, you should not just continue the dive. Doesn't mean you can't hop up to the surface and unscrew it and put a normal second stage on there, but getting a half mask and second stage out of your pocket and plugging it in to complete a dive is not a smart idea in my opinion.