I have both DeWalt and Milwaukee. Mainly Milwaukee now.
Look up Torque Test Channel on YouTube, great independent test information.
Milwaukee is slightly above the rest for impacts, especially the bigger automotive ones, and their nailers.
But DeWalt also has some options that are slightly superior. Their battery grease gun is the best by far.
Daikin is great, Mitsubishi has gotten so expensive recently and it seems Daikin is as good quality.
Agree a recovery pump was a big help. I already had a powerful vacuum pump, but I did buy a recovery pump, cylinder, gauges, and a scale.
You can still check for and find leaks with Better Bubble or similar leak detector.
These are also great to help prevent leaks if you don’t have Nylog and a torque wrench/crowsfoots for the fittings. They’re Teflon or similar. https://flareseal.com/
Anecdotally only, I know multiple people who have done the Mr. Cool DIY kits who have had issues ranging from minor to catastrophic. Some may have been installer error. Some were defective parts out of the box. Regardless, the parts are generally way more proprietary and often only available from the manufacturer.
I decided to go with the more commercial systems and just DIY’d 2 Daikin setups, one 3 ton/4 zone and one 5 ton/5 zone.
You will absolutely need certain somewhat specialized tools. I went as far as to get my EPA license to be able to purchase 410a from reliable channels. Overall the cost was still way less than what HVAC contractors are getting these days.
This is only anecdotal I know, but I am very happy with how the diakin systems have performed.
It’s absolutely more work to not just lurk, but it’s way more fulfilling.
What has he done now?