Excellent service, works for anywhere (they confirmed this to me in writing which I believe is unique for a www flight plan filing service), very rarely fails.
They also correct airways flight plans (to a degree) if you submit something which doesn't go through CFMU.
The only caveat is that if you use it for an within-UK IFR FP, say Goodwood to Bournemouth (really stupid I know) then they will send it to Eurocontrol and EC will chuck it out because e.g. GWC-SAM at 2000ft is below any airway MEA
