My clients had a rather unique concept for a real estate site so we chose RPL and worked with the Realtyna team on a customization project. It turned out a lot of what they wanted to do could be accomplished through configuration items within the FLEX portion of RPL. Emily, Max and Alex at Realtyna managed the rest of the customization project very professionally.
There are a couple quirks, primarily noticeable by people in the United States, but they are easily remedied through language and template updates. For example, the default property template shows the ZIP between the street and the city and some of the field labels use things like "garden" where US people would probably say "yard." This is very easily changed by either updating the language or creating a different feature item in FLEX.
There are a lot of add-on modules priced on an al a carte basis. If you have any questions about what you need you can always contact Realtyna and they'll let you know.
Each part of the software is pretty well documented. It helps to have a working installation when going through the documentation as some things can be a bit confusing if you just read about them.
There is a LOT to this extension, so it is probably better for people who have at least some understanding of how Joomla works. If you are looking to put together an extremely powerful real estate based site, you'd be hard pressed to find a better solution than Joomla with RPL.