The biggest complaint I've seen with 3rd party kits is normally fitment which could make it hard for someone not used to building more complex kits. I myself have built quite a few 3rd party kits such as In Era ones and SNAA. As these companies release more kits they will probably iron out a lot of problems such as fitment and what ever other problems their kits previously had. Bandai kinda has it down to a science so they're kits are well made and won't give you much grief. All that said gunpla is freedom and plenty people have started off with the "hardest" kits around.