I have discovered that a "deep sit" with a high tether will put my back in a bind if I hunt that way for several days straight or for an all-day hunt. If i put my tether about chin high and put my knees at about a 45* angle, it takes the pressure off of my lower back and splits the weight between my feet, knees, and saddle. I sat for 14 hours like this yesterday with minimum discomfort in a kestrel and a set of squirrel steps. Didn't have to change my tether length very often at all, but I did periodically both lean and sit. Never got down from the tree until it was time to go home.
A platform is more comfortable if you stand. If you're sitting or even "leaning" into your saddle it's not putting a lot of pressure on your feet. Knee pads will take even more weight off. I can completely take my feet off my ROS with my knees braced against the tree and sut that way for quite a while.
For me, a platform is not only heavy and limiting when it comes to mobility, but it also is actually less comfortable in the long run because it forces my feet and knees to stay close together.
Definitely try both. You're the one who has to hunt with what you choose, not us. But there's a lot of hype surrounding the predator. I put a lot of hours on the gen 1, and have had hands on the gen 2. It's a good product, but I think platforms are over rated. The comfort and weak-side shooting edge is a bit of a straw-man argument. I have pretty much 0 trouble with both. I think those two issues are very subjective.
If you've got steps on order, it'll be fairly easy for you to use them as an ROS or add a DIY plywood platform to dexide for yourself.