For many, it comes down to Channel Count at programming crunch time.
If I was putting flex strips around a window but just wasn't ready to go over 1000 channels or use E1.31 or multiple DMX dongles, I'd buy the Smart String strips, program my SSCs in single channel mode, get to programming.
NEXT YEAR (famous last words), I could get the software setups and E1.31 all ironed out, reprogram my SSCs and go with pixel mode.