Milwaukee cordless tools all come with a 5-year warranty (with some exceptions). You can use their online eService to send your tools in for Free (they pay to ship) You can also drop your tools off at a Milwaukee Service Center for repairs. They use the serial number on the tool to determine eligibility for 5-year warrantied repairs.
The katsu is considered a cheap knock-off of the Makita by some, others view it as a great budget option. Of note between the DeWalt and the Makita is the different in operating speed ranges, with the Makita offering a lower bottom range and anecdotally the Makita has a better reputation of longevity.