I've typed grep -rn more times than I've typed my own name, so swapping it out felt almost disloyal. But I've now had rg and fd aliased over the top of my reflexes for a few months and I'm not going back.
The speed is the headline and it's real: ripgrep walks a big repository several times faster than grep -r, mostly because it respects .gitignore and skips your node_modules and build directories without being asked. That's the bit that actually changed my behaviour. The old tools would dutifully grind through every minified vendor file unless I remembered the right exclusions, and I never did.
fd is the same story for find. The classic find syntax is a small language I've never fully memorised, all -name and -type f and backslashes. fd pattern just works, with the sensible defaults baked in. find . -name '*.go' becomes fd -e go, and I no longer have to think.
The honest cost is muscle memory. For the first fortnight I typed grep and find out of pure habit, swore, and retyped. That fades. What doesn't fade is opening a hundred-thousand-file repo, searching for a string, and getting the answer before you've finished reading the command back. The old tools aren't bad. The new ones are just better at the one thing I do forty times a day.