Great product, more powerful that the Xero module I was using when I had Xero as my accounting software linked to WHMCS.
There were some small teething issues we had but Peter and team were always there to help with all the questions I had and we eventually resolved them and pushed as updates in more recent versions.
I will be transparent and say that the module is pretty intense and does a lot, there is a lot of configuration you can do that may seem overwhelming at first, especially if you're migrating from one accounting software to another. Maybe video explainer videos would assist future customers.
I also think that some operations do take a long time, for example listing data of a large table when doing a query seems to take forever. I don't know if this is just by design or if its a programming thing (I'm not that technical) but possibly some future optimisation tweaking would be nice.
Overall the plugin is very good, and the support is top notch. I can highly recommend this plugin to anyone who needs Quickbooks integration with WHMCS.