Sorry, I was wrong on the number. For me charging at 32A gives 98% efficiency, at 10A is 88-92%
The difference is explained by the car being powered up while charging, which uses about 250W, a larger percentage of the 10A is therefore lost. If you are low mileage it won't add up to a lot of cost however.
Also worth noting that when pre-heating, the car pulls a little more power than a 32A can supply, so your battery can drop a little, on a 10A UMC you'll lose a lot more miles pre-heating.
If you look at Charging Connectors | Tesla UK you'll see the statement
Tesla recommends storing your Mobile Connector (6m) in the trunk of your car, to use as a backup charging solution when traveling.I guess it's up to your own interpretation as to whether that gives you confidence to use it every day, they are expensive to replace once the warranty is done.
That efficiency matches my experience too monitored via Teslamate.
It works for me now especially via the cost of having a EVSE fitted.
There are 2 50kw chargers 5 minutes from my house if the worst came to it. Longer term though I can understand the investment will likely be worth it.