Tumbler size mainly affects what you can fit into it. As far as I know they all get the job done depending on what media and additives you use. I eventually want to get one big one and two small ones.
The ultrasonic cleaners seem to vary more. A cheap dinky little cleaner gives different results than a good quality unit.
If you plan to do many restorations, get the best you can afford. It saves time in the long run. Welcome to the rabbit hole!