Like with any gadget and accersory (SP) you don't want to become reliant on them, I am guessing you are going to be teaching him to jump, then a pair of boots on the front and back possibly could be a good idea untill he figures out what to do with his legs. Once he is used to jumping, you can probably take them off if he doesnt interfere with himself when he is jumping.
Open fronts are good with learning that way if they hit the jump with the front of their legs they will feel it and wont be too keen to knock the jump again
I personally use open front boots from Greenhawk and would definitely recommend these over splint boots. I love them! They provide good support, stay on well and allow the leg to breathe. Good luck with finding your pair!
*Oh, and polos are good too, but once you get more into jumping, you'll probably want something with more support.