The look of my site is very pleasant with this widget, it's looks great! There are no downsides to using Freetchatwidget in terms that I have found so far (but if you do find something please let us know!).
It has been easy integrating into our own platform as well since we use phpBB3 which integrates easily via codeigniter modules suchas mod_ftpgwamp/modphpbbfwgiftgateway etc.. We've seen an increase traffic from people who come across through search engine results but also those coming directly thru other sites or even twitter accounts looking at specific brands / categories within e-commerce websites like Amazon - So there isn't really any downside just yet regarding user engagement however long term i'm sure they will become more engaged over time.