What's the profit margin for the seller/installer on a product with a retail price of $500 versus $300? Both are going to do the same thing just depends on how much you're willing to spend. Myself, I install a roadmaster in the driveway. Took me 30 minutes. Does what the manufacturer advertised and cost me $200 less than the competing product.
And your question - "Is one any better than the other, and if so, why?" What ever an owner installed is going to be the superior product because - that's what the guy at the dealer or shop recommended, because of the lower cost, because that's what was under the Christmas Tree, because what's what my buddy has, because (insert reason here),,,