Totally newbie: need help with radio module selection

Hi to all, I apologize but I am totally newbie and I’m very confused about radio modules…
I have telemetry board sending data through serial line (point to point), so I bought 3DR modules: one with serial interface (to be connected to telemetry board serial line), one with USB interface, to be connected to laptop and read data.
I am happy: it correctly works at 115200 (transparent serial line), within 100 meters in open space.

To save space I would like to use HM-TRP module but… would it be compatible with my 3DR module?
Are there different 3DR firmware to take care?
If not, I also could buy HM-TRP modules, and write firmware in a second time (if I correctly understand, firmware is open-source, is it?) from SiK, is this right?
May someone explain me, I’m a bit confused…
Thanks, Michele.

What do you mean by “HM-TRP” modules?
In a simple words: 3DR Radio is HM-TRP module (with SiK bootloader) with linear voltage regulator 5V -> 3.3V and a few capacitors and noise dumpers.
Instead of 3DR Radio you can use bare HM-TRP module with replaced bootloader. If you want to connect it to PC - use USB-UART converter (i. e. FTDI).