I've used the site for face-to-face meetings with a few of the huge number of French speakers in London. In my experience, you usually end up chatting for 60-90 minutes, split into 15-20 minute intervals in each language. Once you know each other a little better, I find that you switch between the two languages relatively freely, depending on whether or not you want to practice saying something.
Exchanges go more smoothly when the both of you are at a reasonably similar level and you can continue talking about a topic even when switching languages. It's a bit awkward if a big difference in levels means that you find yourself talking about politics in one language, but about the weather in the other. And it's less embarrassing if you're both making similar types of mistakes!
A good deal of the new vocabulary I post on here comes from conversation exchanges, and I feel like it has been the biggest factor in my development beyond the intermediate level into upper-intermediate/advanced. I've also met some really nice people, including French speakers from Guadeloupe and La Réunion, and a Parisian who is coming to my wedding later this year (shout out to Cécile!).
To prevent awkward silences in those first few exchanges, here are a few ideas for topics to use as starting points:
- why you're learning the language
- what you find easy/difficult about the language
- how long you've been in each others' cities and what you think of them
- tips for things to see and do in the city
- travel in each others' countries
- what you do at work
- share some slang and informal expressions
It hasn't all been plain sailing, and a couple of times I've found myself waiting in a coffee shop for someone to turn up who never does. But overall, conversation exchanges are great. The main thing is simply to go for it. Learning a language is all about talking to people after all!