The muff is more of a distortion/fuzz type pedal almost replacing the amps tone. Overdrive is like hitting 11 when the amp is already set at 10 if we're considering shred. But take example an ehx soul food, blues guys only use it for a hardly noticable boost to sweeten their amps tone.
To be honest as long as its analog and adds some dirt its hard to go wrong. For the sake of testing, I'd recommend something affordable like a used boss sd1, ibanez ts9 or new joyo, mooer...
That Nova should also work but I have no idea if you'll like it, also it might be a bit harder to sell it later. Thing is besides the pedals tone, an overdrive must be selected for the right amp/style etc. too...
I like this video as its educative, might help;
https://www.youtube.com/watch?v=CdKjhXWpjq8For shred, Todd's channel is cool he recently tested the tightdrive from amptweaker and you can hear how it affects the tone.
I'm sure you'll get the idea quickly, but when deciding to buy the first overdrive be aware its almost impossible to nail the right pedal at first attemt. Everybody I know including me changed or are thinking to changing their first bought overdrive pedal
UPDATE:
I've decided to go for a VDL Hotbird to run in front of the GT-001
Lol thats a super aggressive sounding pedal
What I ment was more like getting the clean tone the guy is using on the video, notice the subtle breakup of the amp. Not saying it won't work but situation is like this;
Using subtle overdrive pedals; the tone itself won't sound good or atleast amp-like, but it will work with any amp sim. as it isn't doing much to the tone so you get flexability.
Using strong overdrive/fuzz pedals; Software amp must always be clean to slight breakup, you can tweak the pedals tone but can't jump to alternative distortion tones.
Just give some thought into this, if you find yourself always using a similar tone (and its like the VDL sound) than cool I nowadays only use a metalzone thats boosted with a ts9 or bb9 for shred stuff. But if you still feel like there is some room to experiment then something that lightly drive might be better.