The pricier one has a 40oz. stainless chamber and stainless cutters. The lesser one has a 34oz. composite chamber and stainless cutters. They don't tell you about the composite chamber unless you call and ask them directly. The septic model has the 40oz. stainless chamber and stainless cutters. You don't have to use the additive for the septic version to work on a non-septic system. The Excel has 3-stage cutter system. The others have 2-stage cutter system. I'd get a stainless chamber. Mine has been fine.

Is there any disadvantage to getting the higher priced one from Amazon where it is much cheaper? It's the same one, right?

Amazon is good.

Ah, the vendor does not have a great rating, but there is a thing that says that Amazon guarantees cover the delivery and return policies.

I actually avoid buying anything from Amazon if at all possible, but there is a big price difference in this case.

There may be warranty differences among distribution sources. My two Evolutions, still operating since 2010, were bought discounted, but I vaguely recall that there was some factor that added significant cost from local distributors. Maybe it was non-compete with local plumbers.

Mine was bought off ebay.