You missed out Air Ground Radio Operator (AGRO) that can give an Air Ground Radio Communications Service (AGCS). To get the Radio Operators’ Certificate of Competence (ROCC) is a couple of days of training, costs a couple of hundred quid, and is valid for life - although the owner of the Wireless Telegraphy (WT) Licence at the airfield you plan to give an AGCS needs to sign your ROCC to say they are happy for you to do so.
The only ‘clearance’ that is allowed to be given by an AGRO is a relayed airways joining clearance from Air Traffic Control. Other than that, all they can do is give the information of the airfield, which on calling for join is runway in use, circuit direction and QFE/QNH. It really is “Air Traffic Light” in that they only give information and the Pilot decides what is sensible and safe after receiving that information. The AGRO may offer known safety information, like number on the radio in the circuit if known, and other such like, but shall not give instructions - they are expressly forbidden to do so. In my opinion it is so much better than SAFETYCOM/Unicom as you get an answer and also the latest information when you first start up or join having left the circuit. Of course, if the AGRO is not on the radio then the “XXXX Radio” callsign can be changed to “XXXX Traffic” for times when the Aerodrome frequency is unmanned and if the Aerodrome operator is content for operations to continue.
That, to me, is the best for small light GA airfields - even busy ones. I used to give an AGCS at a grass Aerodrome with over 150 movements a day - no problem.