Crystal, Travelup, Ocado and co are fine if everything goes to plan. You'll be ticketed ok, and you'll have access to most functionality via MMB.

Where it can all go wrong is if there are problems or cancellations when you'll generally get a bit of the old runaround. That said I found Crystal relatively responsive when I had a query.

I have one of the HEL fares, out on A350 and back on A330, late in the year.