Comparing the Lumishore SMX11 and the Lumitec Seablaze X is somewhat of an apples and oranges comparison. The SMX11 looks to be part of lumishore's entry level lineup, where as the Seablaze X is virtually Lumitec's flagship underwater light. A more apt comparison between the two manufacturers, if price is to be considered, would be the SMX11 and the Seablaze 2 (out of production) or Seablaze mini.
For me, I will not mount a plastic light underwater regardless of what they want to claim "space age polymer" it's made of. The SMX11 is plastic... The Seablaze X is bronze. The only plastic underwater lights I've ever used leaked within months (on a trailered boat no less). They were not Lumishore, but I figured I'd share anyway. 3 year warranty vs a 1 year warranty, and now it's no contest. If price is important, go with the Seablaze 3 instead of the X and you will have made up most of the difference, you get a better warranty, and you get a light with an alloy and glass housing. My .02$