My experience is only that of one we have had in to school, so I reckon they are a 17 hh boshie horse in a 12 hh body....
They appear prone to weight gain and are probably fine if worked hard by an adult, but as a kid's pony never..
I also think of all our native breeds they are the ones that retain the "wild" instincts the most.
The one I mention became a very nice ride until returned to his owner, where he instantly reverted to type, clever clever pony brains.....learn quickly who to mess with and who to obey....
My horse is 1/4 exmoor and 3/4 TB. She doesnt look like she has any exmoor until the winter when she is the HAIRIEST thing on 4 legs. The good thing is she never needs rugging (-4 is nothing to her!).