Well, here on OSX, the tool so drastically slow downs the gui, sometimes even beachball. If you scroll thru tracks or sequence. It’s so heavy, that renoise becomes unusable.
I think it’s a renoise degradation bug.
Just a quick thought ffx 
As afta8 says this tool is complicated with lots of notifiers. What I would do to try and narrow down your ‘GUI slow down’ problem is modify the script a little. So I would start to look at line 533, on this copy that I have reads:
notifier.add(renoise.tool().app_idle_observable, capture_params)
Try commenting the idle notifier out and see if that helps so the line now reads…
--notifier.add(renoise.tool().app_idle_observable, capture_params)
Restart Renoise to make sure. Now if it doesn’t help, try commenting out other notifier ‘add’ calls. So lines 548,564,584,588,610,642 (restarting Renoise to make sure) see if that reduces or stops the GUI slow down.
[Edit:] Just maybe worth pointing out that when you disable ALL notifiers via afta8’s method below, technically there should be no slow down of the GUI (although anything can happen/is possible with computer programs.) You’ve got to re-enable the notifiers and isolate the one that is causing trouble. (Also keep in mind that it could be a combination of certain notifiers.)
I think what 4Tey advises will work, but there may still be other notifiers running - Towards the end of the script you will see the following:
-- Add the notifiers (always running in background)
notifier.add(new_doc_observable, open_song)
notifier.add(close_doc_observable, close_song)
If you comment these out then it should prevent any notifiers from starting up - This will prevent the ‘Snapshot edited’ function from working, essentially the notifiers are looking out for any changes in parameter values.
[Edit:] Just maybe worth pointing out that when you disable ALL notifiers via afta8’s method below, technically there should be no slow down of the GUI (although anything can happen/is possible with computer programs.) You’ve got to re-enable the notifiers and isolate the one that is causing trouble. (Also keep in mind that it could be a combination of certain notifiers.)
Thanks, I already tried to comment out each notifier by notifier, but multiple seem to slow down… But I think I missed your’s, so will try soon.