My son has used it, and has quite enjoyed it. I haven’t yet, but I’ll pass on my personal experiences once I have some.
The draw back with iTalki is that you need to have a certain level to begin with in order not to waste someone else’s time - there’s a certain amount of ‘Le café est trop froid’ you need to get through first.
That being said, there is nothing like an actual conversation to both challenge and inspire the language student! I have my first (online) conversation with a Spanish tutor on Monday - I’ll let you know how it goes!