I never wear the sneaker or sandal type of footwear when fishing saltwater unless i'm walking the beach. Then I wear a pair of Teva sandals. If I need specialized footwear, then boots are in order! The extra ankle support and protection against all the various and sundry unusual things one encounters when wading around on flats is well worth a little extra expense. If you can't stand up/walk, you won't be fishing much. Footwear and eyewear are two things I do not believe outdoorsmen should skimp on. The third is emergency gear.

The Simms boots are excellent saltwater wading boots. I can't think of a use for the shoes. I've never had much faith in Patagonia gear (plenty of experimentation) and certainly not worth their premium price tags. But I know nothing about the Marlwalkers.

If you only fly fish saltwater on a "big trip to the salt" type of basis, don't try to cut a corner on footwear! Getting put down for the duration by a foot injury or even really sore feet/legs just isn't worth the risk. Hedge your bets and make the extra investment.