I've cleared Garuda Ex many times, but people struggle with it in DF.
I got a trial roulette with Garuda HM last night, and people wiped 4 times, and then started dropping. The problem with DF is that anyone can do it as long as they meet the minimum requirements, even having no prior knowledge of the fight. Sadly there is no way to check if they have completed it before (at least not until you're in the instance, but it's too late by then), you don't know if they have watched the fight on youtube to get the basics down, and you don't know if they internet connection can handle the instance and the things that it throws at them (this comes more into play with titan-like fights).

1/10, you might get a DF group that can get it together, and down in... but in the time it takes for all those tries and wipes, you could have just gotten a Pf and nailed it by then.