Tried on the DC5 and to be honest, didn't feel all the great. Felt like it was quieter and rev'd smoother but i feel royal purple does a much much better job and doesn't burn as easy.
FEO Ultra is 10W-30 isn't it? I prefer 10W-40 Royal Purple as the DC5 is track and street orientated
I prefer Royal Purple but i guess if you can't afford Royal Purple or Motul etc then you should go for FEO Ultra but i think there's other oils on the markets that are cheaper and will still do the same job.
Use whatever fulfills your needs IMO