I've had a few occasions where I've introduced some ladies to it. In real life, I have Wilderness First Aid certification, meaning that I can help with injuries and problems outside the zone where you can just "keep them comfortable, and wait for the pros". Among other things, I've been to Burning Man, and attend a couple of regional Burns, every year. I've been the First Aid lead for a couple of them. At my first-ever Burn, I was sitting around the First Aid HQ, and talking with a young lady. She was interested in seeing my (legit, not fetish) first aid kit. I took her over to my tent, and opened the kit. She was curious about my rectal thermometer. I pointed out that it was cold out (This Burn happens in February), and I might need to check for hypothermia. I pointed out that the only way to check for core temperature, particularly in someone cold enough to have a diminished level-of-consciousness, was rectal. She said, "Oh - I'm feeling quite chilled, now, can you check?"
I had her lie on my cot, turned up the heater in my tent, and we unzipped her snow-suit. Pulled down pants and panties, and I shook and lubed the thermometer. I slid it in, and she loved it. The sensation delighted her, and she thoroughly enjoyed my moving the thermometer in her bottom. Since this aroused her quite a bit, I opened my fetish bag, and asked if she'd like a bit of relief, via vibrator. I removed the thermometer, checked the reading, and re-inserted it in her anus. Then, the vibe went into her vagina. I pulled out another one, and buzzed her clitoris to orgasm.
As we finished up, she asked me where she could find one of those thermometers (Geratherm rectal, frequently available at Walmart).
SCORE.