I didn't realise there were such great limitations with any of the PS versions, Jo. Thanks for that
GIMP itself is highly frustrating. It has a really steep learning curve, is non user friendly, and totally illogical in where things are put and how to get to them. You just have to learn it 'parrot fashion' from tutorials here or on YouTube (or if you are very masochistic by reading the manual cover to cover). Oh... and yes - a word of warning. Never put something like "GIMP masks" in a Google search bar. Use something like "Using layer masks in GIMP"
There are many things that annoy the heck out of me with GIMP, but I'm not in a situation where I can actually afford to pay for something like PS - any version of it.
The worst aspects of GIMP are the way it doesn't really deal with labels very well, and the vector drawing tools are so hopelessly bogged down with illogical little idiosyncrasies in the way things are done that if I need to do anything by vector I usually resort to using Campaign Cartographer 3+ (a specialised mapping app), or my 20 year old copy of CorelDraw - even though it crashes unpredictably with Win 10. Some of the filters/layer effects in GIMP are destructive, in that they change other layers or even overwrite them, and you don't have enough control to prevent it from happening. Worse - most of these destructive processes are irreversible, no matter how many undo levels you have set for the program. An immediate and current example I can think of that nearly kyboshed my entire challenge entry this month is the outer bevel effect. Fortunately I had only just saved the file, so I was able to close it down without saving it and reopen it the way it was before the bevel disaster occurred.
Filters in GIMP are never 'live' as I hear they are in PS - if you use a bevel filter, or a shadow filter on a layer in GIMP it doesn't update if you update the drawing on that layer, so a lot of the work I do is guesswork - anticipating how a layer will eventually look with a drop shadow on it because I can't add the drop shadow until I've finished the drawing on that layer.
What I've said sounds very disparaging, but its the absolute truth about my personal experiences of GIMP over the last 4-5 months since I started using it. As for why I continue to use it despite being really unhappy with the way it works? Its because I have managed to adapt my methods to cope with all these little difficulties, and I really can't afford the monthly rent on even the cheapest version of PS. Other free programs like Krita crash too frequently on my machine, or present me with yet another steep learning curve in order to be able to use them as well as I now use GIMP. So - better the devil you know, than the devil you don't!