I got a small Diva Cup for my Long Trail adventure in September hoping I could get some practice in, but my period is irregular, kinda heavy at first, and has this great habit of coming on the day I start a 3-day backpacking trip. So, I had no choice but to try it for the first time on the trail this month. And it was pretty great.
It was bigger than I'd expected, but pretty easy to get used to. I used the basic U-fold and it wasn't difficult to insert even in backcountry (for some folks it's easier to prop one foot on a toilet/privy seat/log), and it stays low enough that you can grab it and remove it without too much hassle. Just go slow, and hold on tight if you're using a privy! It was a little messy, but it was less than expected and overall less mess (and less cleanup time) than pads have been. I just made sure to keep some water in my Sawyer squeeze pouch with the filter attached, propped it in my elbow with the filter cap open, put a couple drops of soap on my hands, and bent forward to tilt out a stream of clean water. Maybe it's overkill, but to me it's worth carrying the extra weight to be able to properly wash my hands.
There was some slight intermittent cramping for the first hour or two after inserting the cup, but I expect that will go away with more use. I also used panty liners, which I'll definitely continue to do to protect against leakage. When the cup is near capacity it starts "burping," so you can tell when you need to pull over. It happened once, but I was usually fine waiting until I got to camp, then emptying in the morning. I'm definitely taking it on the Long Trail with a handful of panty liners, plus the spare pad in my first aid kit that doubles as nonstick gauze.
Note about IUDs: I've seen some concern online about using the cup with IUDs, thinking the suction can pull it out. My doctor said it's probably fine, as long as you don't accidentally pull on a string when you're removing the cup. They can cut the strings back, too.