I tested Boldbeast Call Recorder on the Redmi 2 with CyanogenMod 12.1 and with MIUI 7.
It did not give good results with CM12.1 (cm-12.1-20150926-UNOFFICIAL-hm2014811.zip). After trying 30 different configurations, I contacted Boldbeast service which suggested
- Record Mode: 1
- Tune Audio Effect: No
- Tune Audio Route: Group1
- Change Audio Controls: Yes
- Change Audio Driver: No
- Start Input Stream: test Yes and No
There was a strong 5sec screeching noise at the beginning of the recordings and just ok after. It seems to be a generic sound problem with CM12.1 for the Redmi 2. The noise may actually be added during the playback and not during recording but I have not investigated it.
With MIUI 7 (wt88047_global_images_V7.1.1.0.KHJMICK_20151209.0000.6_4.4_global_a49c63ee30.tgz), the recordings are very good with the default settings. The quality is actually a lot better than with the MIUI7 built-in call recording features.
It seems that (at last!) Xiaomi released the kernel sources for the Redmi 2 two month ago. So the sound support may eventually improve with CM for the Redmi 2.