I can vouch for the quality of the Mission Engineering pedal. I have the LP6 and it's great.

The Variax connection is not the same as the FBV pedal connection. PODs only have Pedal connections (they dop not take variax connectors), and Amps have both a Variax and a Pedal connection. The HD500 already has pedals, that's why there is no separate input for the FBV pedals, whereas the PODs and Amps do not have pedals (except obviously, the X3L and XTL which again, do not accept FBV pedals).

I don't regard this is a mistake. If you really want additional external controls, this can be achieved with an external midi controller pedalboard.

David.

I believe any expression control pedal compatible with a TRS 1/4" plug will work just fine.

Unfortunately, this isn't true. Most expression pedals actually won't work with the Line 6 stuff. You need a pedal that has a pot value close to 10K ohms.