Most probably they will be on rootstocks that would eventually make them grow to about 10ft height and spread (depending on soil quality and rainfall).

But if you prune them very hard every year, in early-mid august (cut back all new growth to just a few new leaves), you should be able to keep them in containers for many years. Due to the strong rootstocks, they may be best not fed too much!
You may want to winter-prune then for the first couple of years, to get a good framework going that will produce a nice shaped bush in later years.

You could easily pay four times as much for one on a pot-sized rootstock (e.g. M27), so it's probably worth a go trying to hard prune these cheapies.