Fitness tracking (power meter)

Hey all,

On a regular bike I tend to track watt/kg output as a good measure of fitness progress, but obviously this doesn't work so well on an ebike.

I'm looking at installing a power meter on the ebike (when it arrives!) but I'm having a hard time finding one I know will be compatible with the bafang ultra. I'd also like to avoid spending $1000 on fancy power measuring clipless pedals.

Here's my short list:
- Watteam Powerbeat ($399) -- Crank arm conversion. Might work? but obviously it doesn't list bafang crank arms on the compatibility list.
- IQ squared ($300) -- Pedal conversion. Seems like a good universal solution but doesn't ship until Nov and is a sketchy indiegogo campaign.
- Zwatt Zpider ($360) -- Crank arm replacements. Will it work? No idea!
- Garmin Vector 3, PowerTap, etc. ($800+) -- Clipless pedals. Should work, but more expensive than I'd like. I also prefer to ride platform pedals on a full suspension bike.

Anyone using a power meter on their bafang ultra?