Just finished the Kaplan online practice test and review seminar - overall I thought it was very good.
The best part is the handling of the test itself. It runs pretty much as the GMATPrep software is presented - standard blue layout, question / answer formats as they are presented in the real thing - a good range of difficulties too. The advantage here is that you get a good breakdown of where you went wrong, how long each question took you (good to spot those questions that take 7 minutes where only 2 are available!) as well as answer explanations in a follow-up email.
Of value, but less so (I found) is the interactive session a few days later with one of their instructors, in the company of several other students (also attending online) - which is a format representative of their online teaching environment and so useful for those contemplating this method of tuition.
I found the session was well delivered, both technically (streamed online) and professionally, with a friendly instructor who (whilst obviously having done this many times before) really handled the session well, even when students (i.e. me) chip in with comments during the session.
The only down-side is that relatively few pre-selected test questions are touched upon in this session, as the time allocated for the session is 90 minutes, the remaining portion of which runs through their standard explanation of the GMAT format which I've now seen a good few times at other events.
That said, I did spot a new way of analysing the question types, a way which would've saved me about 10 minutes on my answer-time (getting all the answers down in the time limit is now looking much more achievable). In summary, it's another great free opportunity to get a practice test under the belt.