My comments below after tried few hours:
- GT3B/C receivers are not compatible
- FS-iR4 receiver costs approx. RMB 120 which is OK.
- no price from TaoBao for sensors yet.
- SPD01 uses magnetic detection but require to purchase a separate magnet elsewhere and attach to wheel or spinning gear to detect rpm, kind of awkward. Better if it can attach and detect magnetic field change from motor like Yeah Racing sensors for MT4
- SPD02 uses optical detection, no high expectation
- the temp. and voltage sensor are OK though
- Transmitter touch quality is adequate but don't compare to Samsung/iphone
- some nice features, eg:
- can select and order up to 4 sensors to show on main screen
- you cannot turn off transmitter before turning off receiver
- has auto power off after idle for a definable period (with audible alerts)

May have more interesting findings after install on my short course truck later.