I have a climber and several Alpha hang ons. Used to have a few Assaults but sold or traded them for the Alphas. Agreed that the platform size is almost the same, so is the weight almost the same. I often stay on stand from dark to dark, 11 or more hours. During that time, I spend sometime standing. That's where I find the Alpha more comfortable, versatile than the Assault. Just a little more room for my feet and to move around and get shots toward the back side of the tree. There's not a big difference. You'll probably like either one.
I don't use straps between the hand climber and platform on my LW climber, so there's no problem tipping up the seat. The climber platform is the same (size) as the Alpha hang on. It's just an Alpha turned into a climber.