Do you mean as in the "Baby Ballet" franchise? If so, it's absolutely fantastic! It's not a proper dance class at all, it's mainly just lots of movement and singing, with the occasional inclusion of what could be the basics of ballet moves later.
We go to um... I think the class is called Tiny Toes, and started when Roo was 18 months old. She went through a phase of just wanting to run around after she'd been a few times, but that only lasted a couple of weeks, and now she loves it. We got her the outfit as an early birthday present, and she gets really excited when she sees her "Baby ballet dress!".
If you look on YouTube, there's a video of something like "Kitty goes to Baby Ballet" and it shows a couple of clips of what they do in class. On Saturday just past, we had a mixture of jumping, waving scarves/throwing and catching them, marching, action songs, ring songs and playing the tambourine. It's brilliant fun, and I think good value for the money. One of the main things that drew me to it was simply that it's on a Saturday for us, and it was really difficult to find baby/toddler classes which meet on a Saturday!
I'd definitely go for the trial, and I hope you and LO like it as much as Roo and I do