I have twice. Like you I've had the fantasy for a while and finally got to fulfill it recently. First experience was in Barcelona this past summer. Was a hot muscle bottom from sniffies, the first time I would meet someone from that app. Was the 2nd guy to load him up that night, I got to his flat about 15mins after first guy loaded him up. Door was open, I walked in and he was laid face down ass up in his bed wearing a jockstrap. Felt his used hole with my fingers, hole looked glazed and could see traces of the first guys cum. Got rock hard and slide my dick in without lube, felt sloppy and warm. As I fucked him harder the first guys cum kept gushing out and was all over my dick and balls. Then pounded for a while and gave him my load. After I left we chatted and he told me he took 3 more loads after me making it 5 lol. Also, The city has quite a number of cumdumps, anytime you open Grindr or sniffies you are sure to see at least 5 cumdumps looking for loads. And most are hot muscle guys.
2nd experience was about 2 weeks ago in London, this was a proper no loads refused cumdump. He had it on his Grindr profile to say he's a visiting cumdump looking for tops. He hosted in a hotel, was the 4th guy and the hole was really sloppy and cum kept gushing out and was all over my and dick and on the bed. It was kinda gross and hot at the same time lol. The gross part was there was the somewhat offensive smell that was oozing out. I think cum smells funny after it's dried up lol. It wasn't bad but I enjoyed 1st experience more maybe cos the guy was hotter lol.
It feels good, would try it again but definitely not something I will do frequently