Yes, my MBK is using his UV light on daily basis since the day he got it (I put a T5HO 6% of arcadia over 60% of his vivarium). Now, during the day, he's laying out and basking instead of laying under his rock until lights out.
I intend to extend the provision of UV to all other snakes as well. But first need to organize them all into a new furniture because right now they are standing all over the place.
I'm waiting the new furniture to arrive, then can put my MBK in a bigger vivarium (he's almost 90 cm now and vivarium he's in now is 80 cm... it's big enough but I like to give them space). Then a few others can move one up in size as well as his vivarium becomes available. The other vivariums are now featuring 'basic habitat features' (= normal snake bedding and stuff to climb on/under, heating, etc... no bio-active and planted right now as I prepared for moving them all).
I have all plants ready for the big planting day and most lights. Just need to purchase the UV still... debating with myself if I should supply UV to my albino milk, and if so, how much.
PS.
As for the debate whether or not it is required. No it's not required per se for rodent eaters. But UV helps them, they use it and seemingly like it (as they seek it out). UV helps with immune system, it's not just about D3 synthesis (ie- just like in mammals). So given that a) you can; b) they seem to appreciate it; I see no reason not to do it. The only real thing you need to care for is that you do not provide too much and you give the reptile the opportunity to NOT have any UV. So there should be a gradient to a 0 or close to 0 UV index in the terrarium, and places where there is shadow, even directly under the UV so they can regulate their intake. One should not force it upon them, so to speak.
PPS.
Danny, that Olive in the lower viv really seems to have quite some attitude

Must be a handful at times heheh