I have the Reebok board and it is very well made and works great for what it is. If you have decent balance already, balancing on two feet will be pretty easy and not a challenge. Balancing on one foot is more challenging but not that difficult either, however, you can do things like one legged squats on it which greatly up the difficulty level.
Haven't used the other one but I did build a homemade side to side balancing board similar to this one:
It is quite a bit more challenging than the Reebok circular type balance board at least for me. I have trouble staying on it for any length of time and don't even try to do stunts on it, however, I have zero skateboarding or snowboarding skilz so someone with those would probably not find it nearly as difficult.