Dealt with both of these companies, never had a problem, except for a broken maskbox with my Cressi Big Eyes mask - emailed LeisurePro and they dropped a free one into the mail the next day. Couldn't ask for more. Expect to cop a customs duty invoice from DHL if you order stuff from DiveInn and the order is over $200 - but it's only 4% or so. It worked out about $20 on a $500 order I placed with them.
Haven't dealt with Simply Scuba, but from what I gather they're reputable. Contact each company individually, or check out their websites, for warranty info - basically you're covered by the place you buy from rather than the local distributer. But warranties generally aren't a problem - there is a thread going at the moment somewhere with a poll regarding warranties being required on new gear - do a search for it, and judge for yourself if you're happy with the chances of having to deal with warranty issues via mail.
cheers
Ben