I just don't see the point of selling an X5 and X7 that both share essentially the same features, but only changes the size of the form factor.
I think it would make best sense to at least phase out the oversize model, make both use the same 'small form factor' but just add premium features like at least "save states" and 'cheat system' onto x7. Those appear to be at least the standard add-ons to the GB X7, and Mega Everdrive X7 for example.
I don't see why X7 should 'cost more' if all it does is change form factor, and doesn't add anything new to flashcart. Presumably there would be no reason to have an x5, if both were exactly the same, other than 'form factors'. Small form factor for all (including a cheaper 'x3' (no rtc?, no real-time battery save? (see GBX3)), would probably make the most sense.
However, until I see a good 'x7' and see what features it has. I'm fine with my X5, and I've bought Omega to test out. I have more than one GBA or DS option, so I can also take advantage of multiple Flash carts such as for using for game linking between consoles or Gamecube, so I still feel like its an investment.