Over all 6.1.0 seems to working OK depending on how complex rules you have. Simple page restrictions are working fine for me. However there are still some issues as you can see by reading these forums.
Myself I’m mad enough to update to 6.x since i don’t use this plugin on any “real company page” and only use it for a gaming page.
My personal opinion is that if you use this on any real site where revealing sensitive information may harm your business, you should maybe wait a bit longer until more bugs are tackled and keep using 5.11. If you use it on a less sensitive site and have only simple restriction rules like the page restriction rules the 6.x good for that. Keep in mind that if you are looking to update to increase your sites security there have not been any found security issues in 5.11 and since 6.x is a complete rewrite of the plugin in my opinion its more likely to get these security vunerabilities. So all in all if you run a sensitive site keep 5.11 until security issues possibly are found in it and if you run a less sensitive site you can swap to 6.x and keep on receiving updates as it goes.