I used this extension for few months before writing this review.
I also bought a dedicated server to run jomres, I've been using Joomla for several years for several projects and clients.
-Cheaper than other similar alternatives, only in monetary terms. You will end up spending endless hours to figure it out.
-Learning curve: it takes a long time to learn how it works, adding businesses and setting up rates is complex and confusing for a travel agent or a business owner compared to other booking systems.
-This is not a Joomla extension, it works with Joomla (sometimes) but it's more like a standalone booking system, it was built for Mambo and after integrated in Joomla and now also in Wordpress.
As a result, you should manage Jomres from the frontend and a very annoying additional menu is added to your website.
-Conflicts with other plugins or extensions, since it's just integrated in Joomla there are several conflicts with plugins and other extensions.
At some point Jomres crashed the whole website during a version update. I've never experienced something like that.
-Website will slow down and yes, even if I had a dedicated server.
-The design is outdated and basic however you can't use overrides. It must be the Jomres way.
In conclusion, I was not impressed at all and I'm not recommending it.
If I can't take advantage of all the Joomla extensions, if I can't easily change the design, if it's just a standalone booking system integrated in Joomla, I had to look somewhere else and I found it.