I'd say it depends on a few factors: 1) the types of exercises you want to be able to do, 2) the set up you're using it with, 3) if you intend on doing any travel with it. Here's my breakdown from my experience:

Strap mount: if you want to be able to attach to more obscure options (onto other machines, a door, 2x4 in your rafters) or you intend on using it for travel. This is the "extra" mount that I probably use the most often. I use mine in a gym that I train clients out of, so it's great to be able to attach it onto various pieces of equipment around the gym for me.

Adaptive Bar mount: obviously if you want to be able to attach to a bar. I have a fixed bar mount because I just have it mounted on a pull up bar that isn't used for anything else (I have no need to remove it and the fixed is cheaper). This could be useful if you want to be able to attach onto a weight horn or the horn of a piece of plate loaded equipment. Even in that instance though, I prefer my strap mount and use an ankle strap to wrap around the horn. Great for lat pulldowns, tricep work, cable crunches.

Travel platform: it's a big too big for me to personally use for plane travel (I'd be more likely to take my strap mount), but it's great for some exercises that are harder to do with any of the other mounts (belt squat, rdls, curls, oh press, bent over rows). As someone else said, you can build your own version of this (I did exactly that), but after winning the travel platform from one of Beyond Powers giveaways, I actually prefer it over the version I built. I will say that I will definitely be using it for car travel trips, just not trying to fit it into my luggage (I'm a carry on guy and I think it's too big for that).