OK, the lap belt & diagonal restraint may be simpler to use and operate for passengers but a four/five point harness is hardly a difficult concept.
A pilot should always make sure that his passengers are correctly strapped in and, if they can remember old car seat belts of the 70s, they should grasp how to use them; although the mechanism on Squirrels is v. fiddly IMHO
. I know which I prefer.
Cheers
Whirlygig