This P22 rootstock has really started to take over from M27 as being a dwarfing rootstock for apples. It is being used commerically, growing to 1.5m - 2m and its is very cold hardy. Slightly susceptable to fireblight and wooly aphid, but all round it is better.
These are 'Grade B' rootstocks, and as such may have very little root growth and be small in diameter. There is nothing wrong with them, except they may need an extra year in the ground.