Adaptors that let you fit a ES lamp inna BC socket are extremely useful, but should be regarded with a degree of caution, as the outer part of the ES screw can become live due to the polarisation roulette inherent in the BC socket. Good adaptors enclose the entire screw part to prevent accidental gefingerpoken, but not all of them do.
Personally, I consider them Mostly Harmless for ceiling lamps, as if you're getting a ladder out, you're in a mind to think about safety. I'd be wary of using one in a table lamp with a switch on the holder, thobut.
Pragmatically, I think we should admit defeat and install ES holders wherever possible. The BC fitting is nice, but it's basically BRITISH exceptionalism at this point.