I have a reasonable quality crimping tool and a box of red/yellow/blue terminals.
Define reasonable quality. Did you get it off the Snap-On truck or from Home Depot or random auto parts store?
Honestly, there are so many crap crimp tools out there you could fill a dumpster with them...and that's just different brands.
Personally, I use what ducatiman pictured on occasion but I have another similar tool that I use just for stripping the insulation off the wires I'm working with.
For actual crimping I use one of these:
It's from Klein tools and you can find it at either Home Depot or Lowes in the electrical section. There are several models of this type, some with a single crimp hammer and anvil and some with two. Mine is single but that isn't what's important. The hammer and anvil is what is important. If your crimper looks like this:
I would consider it wholly unsuitable for real electrical work. Note that the crimping portion of the tool does not have a hammer and anvil type crimper.
Using a hammer and anvil style crimper, it is possible, even with cheap terminals like you'd get at any auto parts store or even Harbor Freight, to make passable and effective repairs. Your terminals won't slip right back off but you can't wuss out when crimping either.
It takes a fairly firm squeeze of the crimper to get the job done. I mean, unless you get a set of ratcheting crimpers like some of the pros I've worked with used. They are not cheap however. I mean, if you went with a Klein anyway.
A Klein will set you back around $160. You can find them cheap on Amazon though. I've seen them there for anywhere between $15 and $160. Depends on how high a quality tool you need.
If I were doing electrical everyday and my pay check depended on that, I'd likely get the Klein tools. I'm not an electrician and I no longer work in heavy equipment repair so I just get what seems reasonable to me for my garage. The Klein crimpers I first posted were like $17 at Home Depot when I got mine 25 plus years ago. That said, you can find them from Husky or Kobalt at either big box store for under $20 still....sean