So I should mention for the OP that he should also beware of what he's buying if hes buying used. I just picked up a diverite backplate today and it does not have cam band slots. I knew that going into the purchase and will be getting an STA to go along with it which I can fine with.
Hell I didn't even know that diverite made backplates without cam band slots! But hey whatever.
LOL. Yeah, my cave diving buddy got in a pissing contest with a buyer on EBAY when he sold a DR plate that had no slots. Fact is he had no clue what the buyer was talking about because he did know about the STA-less internet phenomenon. He dives doubles 99 % of the time.
Plates were developed for use with doubles. Although there were some plates with "two" sets of slots to be used with 2 pairs of straps (don't see to many though), the most effective way to carry doubles was to bolt the banded pair to the plate through holes eleven inches apart.
Then, to adapt the plate for singles, the most effective way was to bolt a STA to the plate. Halcyon plates and wings did not have slots either.
The internet phenomenon started I guess when the early STA's were 5/8 inch deep channels designed to receive lead ballast. Today there are many virtually weightless STA's in the 1/8 inch deep range.
However, it still seems to be a big deal to say "no STA required". As with doubles, the rigid application of a STA for single tanks is an advantage IMO.
In response to this internet phenom, I think all manufacturers have developed systems which "don't require a STA". yippee.