Remote SLR lens body phone thingies enlighten me

[cptsideways]

I'm not sure what their technical term is but a friend had one, its was a DSLR body/receiver that you attach a lens to & it connected to your phone via wifi or BT I assume. It was not a full camera, quite neat it also had an SD card for when your phone was not connected.

It looked like an ideal thing for me, being compact but I forgot to make a note of what it was!

Are they any good? worthwhile? better or as good as a camera?

[Kernowlokal]

These things?

https://www.sony.co.uk/electronics/attachable-lens...

I saw them a while ago and thought they looked okay, but then saw the price and you can get an okay compact for that or a second hand DSLR.