winged c 6550c is not good for ref 5se??

I ordered 3 of svetlanan SED winged C 6550c from 'Upscale audio' last week and it was not shipped until today, so i call them to find out what is going on here.
They told me they didnt send it because " This tube is not going to work well with your audio research amp and it will failed almost every time".
Is it right?