Maxxus or Marmox solid shower deck & tanking? Advice and recommendations please :-)

[longdraws]

Please help me with which is the best product to use. I hear that Maxxus does not need underboarding but Marmox does and it is considerably cheaper.
I have a 1500 wide space by 800 (to the shower screen). Should I get the full deck 1500mm or the smaller 1300 and tank the remaining area. The 1300mm wide deck has a waste that is almost in line with the existing so would seem better.

Any help or advice most welcome please.

Ldraws