A chargepoint, whether tethered or socketed, contains electronics to tell the car how much power it can safely draw, and several safety features - ensuring that the cable is not live until after it's confirmed to be locked into the car, verifying earth continuity etc.
If you take a Tesla UMC (the 'mobile connector' currently supplied with the car), plug it into a blue commando socket, and never unplug it again, you have got a setup exactly equivalent to installing a Tesla WC in the same place - but more expensive (the UMC costs more than the WC), less weatherproof, and less expandable (a key feature of the WC is the ability to chain them together to share a limited supply if you have a second EV).
So the commando socket is only cheaper if you have a UMC "for free". It's a very poor option for your main home charging, as you really want to carry the UMC in the car at least on long trips, so either you unplug it and roll it up to take with you every morning, or take it "only when you need it" and end up forgetting it. Also, it's good not to rely on your UMC for daily charging, since if it breaks (more likely under daily wear & tear) you are then stuck, whereas if your home chargepoint breaks you've still got the UMC to plug in to a 13A socket for emergency use.
However, it is an acceptable second best (and better than just using a 13A socket) for places you visit infrequently and can't justify the cost of a proper chargepoint. Note that a commando socket installed for EV charging is required to follow the same regulations as a chargepoint (section 722 of the wiring regulations): it doesn't cost much extra to do this stuff properly, and does mean that you can later swap the socket easily for a chargepoint at a later date (eg. if the relations also buy an EV).
