I have purchased a few kits from them and nary a problem. The helmets are actually produced by a separate individual, Timeslip is just handling the ordering for that person. The quality of the helmets is supposed to be outstanding.
His Season 1 helmets are very large - so if you have a big noggin, this is perfect. The season 2/3 helmets are much smaller but can still accommodate big heads up to a certain point.