If each domain brings up different content on a different domain name then there's really not going to be any problems.
Even though it goes to another "landing page", then as far as the visitors are concerned they're seeing a unique site. So, there really shouldn't be any issues--promote each site/domain just like you would any other website (i.e., get on-topic links, submit to directories, etc. etc.).
As long as you don't link each "site" together and as long as you promote them separately and they don't have unique content then there really won't be any issues/problems.
If the actual product page on site A and site B includes the same content then there will be duplicate content issues--one site will end up showing up in the index and the others will be discarded/ignored.
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