I have one of those small blue bluetooth ones lying about, I think it was around £2.50 direct from China a few years ago.
At the time, I bought it to work with a Ford using the J1850 PWM protocol but it wouldn't connect to the ECU - despite the protocol being listed in the spec. I took it apart and found that the pins weren't even wired up for it - different protocols use different pins in the OBD plug. It does, however, work perfectly with the Jazz.
The car had no MPG-ometer, so I was going to set up a similar device to the Scangauge, connecting it to an Android app such as Torque, or there are some other apps which are very similar indeed to Scangauge. The OBD hardware for the Scangauge is basically one of these, connected to a bespoke unit with the software and an LCD display.
I have collected various diagnostic tools over the years, all clone type laptop cables for VW/Audi, Nissan, Peugeot/Citroen, etc., and a couple of generic OBD readers too. I couldn't begin to guess how much these have saved me over the years.
Although those cheap generic ones will only access live engine data and trouble codes, and not the other systems on a Honda such as ABS, gearboxes, etc., I would say it would be the best £3 you will ever spend.