I recommend buying the K6 and using the savings to purchase the 710, 7300, or 705.
There are two ways to solve the problem of slow charging for a 5DR battery: either buy a charging dock, which takes 3-4 hours to fully charge, or purchase a Type-C compatible 5DR battery from a third-party seller. In practice, Type-C compatible batteries are more convenient to use and have a larger capacity than the official batteries. After being fully charged, they also have slightly higher voltage, unlike the official batteries, which lose voltage quickly after just a short period of use.
Regarding quality, my 5DR has been repaired twice already, and both times it was due to screen issues. However, the official after-sales service was very good, and they were able to repair it quickly.