I don't have any personal experience to back this up, but my suspicion is that self-made deck would likely work
less well for reading with. Ever since I started taking a serious interest in Tarot, I recognised the main thing I was hoping get out of it - advice from an 'outside' perspective. I've never formed strong opinions on whether "what the cards say" is all provided by my subconscious, or whether I'm being guided by some greater power - what's important is that it comes from something that's not my deliberate, aware,
conscious train of thought.
Creating my own deck would strip away one important aspect of that. When I read a deck created by someone else, I get their perspective on each card. This is why I really like having several different decks! - because that perspective is just a little bit (or sometimes a big bit) different with each one. Even those that are generally classed as 'clones' in the same tradition (e.g. RWS, Marseilles, Thoth) will have a slight shift in focus - even if the very lineart is identical, the shading can change the way the card feels. (Case in point, I
posted just the other day my feelings on the Radiant RWS I bought to replace the original-style RWS I first owned).
When I use the cards, it feels like looking through a window and seeing something outside of myself (quite literally: that's one of the reasons I don't care much for borderless decks - the border to me is the 'window frame'). With a deck I'd created myself, it would be more like looking at a mirror, seeing only aspects of myself reflected back at me.
(...And yes, maybe that says more about my limitations and lack of imagination than anything.) I do wonder, how many people who've created their own decks find they use them primarily/exclusively over any other decks they own?
That said, I do think that creating a deck would be a really valuable thing to do, as an exercise in learning more about the cards, and potentially as a tool for discussing your interpretations with other people. And while I probably wouldn't use my hypothetical self-made deck for primary readings, I might well use it as a 'reference', for clarifying readings I've otherwise struggled to interpret (similar to how I sometimes use my RWS, as mentioned in the aforelinked post).
Regardless of whether I used it, or how well it worked, I admit I'd love to own a self-made deck: shame I have no artistic ability whatsoever.