First up I will point out I'm not experienced in anyway with regard to hobby radios, hence why first radio I tried didn't work

Here's what you get.
Here's a pic next to a battery to show the size
The way this adaptor works is you connect a 4 channel (or more) receiver to the RC2HL (see above) and then the RC2HL to the RX13, 14, 18 by simply switching the HL receiver lead to the RC2HL. Like this.
Simply enough? Well there is no instructions which come with it, not an issue if your ok with hobby radio gear for me with no knowledge it means double checking the leads are the correct way round etc. If in doubt check out the RCTA forum which has lots of pictures and diagrams.
Next problem is not every radio works for the hassle I had I can only recommend buying a radio which is known to work (listed on product page when you buy the adaptor). For info I can tell you Planet T7 with either R6M or R7M receiver does not work.
Final issue is connecting the 4 channels correctly between the RC2HL and receiver and finding the correct normal or reverse for each channel. That one is a going to be a bit of trial and error as each radio is different.
One last thing is because your new radio doesn't have a start, machine gun, or K button these are mixed into the control sticks. For example start is left thumb stick down and right. Machine gun is left stick fully down and gun elevation is left stick half down. K button is left stick up.
So having got through all the setting up. How does it work? Well great, tank is as is with a HL controller but now you have the advantage of better range and no interference so should work great where there is great number of other RC vehicles. Plus it is only a 30 second job to switch between tanks which means one controller for all your tanks presuming you only use one at a time.
Ian.