TH5402 HD is a closed source non-linux box...so it's inferior to DM800HD and it's clones.
Linux recievers have far more features and flexibility, plugins, 7 day EPG's, Enigma 2, Choice of multiple images etc etc..
I usually find the total opposite !
The linux'y open source boxes usually have pretty crap and badly written flaky software that barely functions in any coherant manner whilst most of the closed source boxes have firmwares which tend to work reasonably well (maybe not straight away but usually relatively quick if they want to continue selling).
Its got to be said that linux really isn't the best OS for embedded systems. Its way over-bloated for what it does although it does have its uses !