For whatever it's worth, my experience is that if you're working in a darkroom with a counter, stainless reels are really easy to load in 35 mm -- get the film into the clip and correctly bowed to fit between the two spirals, and just push/roll the reel away from you; the film will almost automatically go into the reel. I've never used stainless for 120, but I'd expect to have much more "fun" because the film is more flexible than 35 mm.
If you're doing your loading in a changing bag, stay away from stainless reels -- I can't load the things unless I have a flat surface with open space above/around the work. A dark box or changing tent would probably be okay. Honestly, any loading in a changing bag can be a challenge compared to a nice, flat counter top where you can stand up, move around, take a hand off the reel/film to reach for something else, stick that piece of tape you'll need in the dark on the edge of the counter, etc. I saw a YouTube video recently on making your own collapsible changing box -- you can use sleeves from a winter coat with elastic cuffs, or cut from a small/cheap changing bag, and the box itself gives a flat interior surface to work on and room above the work, rather than lying on top of what you're trying to do. If I weren't going to have a real darkroom within a couple months, I'd have to revisit that video.
BTW, the smaller Paterson tank, that holds 2x 35mm reels or 1x 127/120 isn't that much of a limitation; you can load two rolls of 120 into a single reel, and develop them with the same amount of chemistry as two rolls of 35mm. The reels were built to take 220, which is twice as long as 120, so there's plenty of room on the reel. I generally load the first roll normally, and stop when it's all through the ball bearing ratchet. Then I push it about halfway around the reel, but less than a full turn, and start the second roll. I run the second roll on until it reaches the tail of the first, and put a (precut, in the light) strip of masking tape or preferably darkroom tape (which will stay on when wet) where they meet. This prevents them overlapping while I finish walking the second roll in, pushing the first down to the core of the spiral. Some folks will, instead, manually push the first roll all the way in until it stops, then just load the second normally, but it doesn't take much to get the second roll overlapping the first; I prefer to tape them together to prevent that.
One major advantage of the "three reel" size Paterson tank is that you can buy an adapter for it that will hold six sheets of 4x5 or 9x12 cm film in the same tank. Handy, if you think you might get into large format later, but not really worth the money unless you'll also need to process three rolls of 35 mm at a time. For about the same money as the Mod 54 unit, you can get a Stearman Press 4x5 daylight tank (they're a sponsor here, and have their own sub-forum in the Analog section) that will process four sheets in half the chemistry as the large Paterson needs for one or more.
