This. As for whether it's good or not that sort of depends on you're looking to do, I've not looked at it for a few years but last time i did it essentially packages what can be done yourself into a single program that's easier to use.
Personally I've not been a fan of NTlite ever since they went down the freemium route, I've got nothing against them doing that as there's a ton of work that goes into such a program and bills have to be paid, it's just like all the programs that modify a based Windows install ISO they're not really doing anything that you can't do yourself if you have the time. (Although an even longer time ago when i tried the free version of NTlite it does use some non-Microsoft ways of modifying the image so i guess it's a more extreme version of MSMG toolkit).
FWIW what got me into making modified unattended Windows ISO was
Win Toolkit, the dev abandoned it 4-5 years ago due to time constraints so i wouldn't advise using it on anything newer than Windows 7, but it gives you a good idea of the sort of things you can do to a Windows image before installing it.
e: MSMG would be my recommendation for people with no experience of modifying Windows images because IIRC their ethos is to not allow the user anything that would break Windows and only use official methods of modifying the image. I wouldn't touch pre-modified Windows ISOs like Tiny Windows or Ghost Spectre with a bargepole due to the nagging thought in the back of my mind that IDK what they actually did, if there maybe a time-bomb in there somewhere.