Summary
Hartenstein made a somewhat bold bet in the summer of 2021, opting out of his guaranteed minimum contract with Cleveland. It looked to be a mistake at first, as Hartenstein had to settle for a non-guaranteed minimum contract with the Clippers. However, he made the roster and had a very nice season with the Clippers.

After years of putting up nice numbers in the G-League, and getting a little bit of time with Houston, Denver, and Cleveland, Hartenstein has now established himself as a quality backup center through his play in Los Angeles.

Hartenstein has nice touch, as he has the ability to hit floaters as the roll man. He can also find shooters if the defense collapses. Hartenstein is also athletic enough to be a lob threat. He has good offensive rebounding numbers, having an above-average offensive rebounding rate each season of his career, according to Cleaning the Glass.

Defensively, Hartenstein puts up good steal and block rates, and also has some legitimately good rim protection numbers

Hartenstein hasn't been able to extend his range to outside, and he fouls too much, but overall Hartenstein has shown he can be a serviceable backup big, and possibly even more than that.
 
Cap Considerations
Hartenstein will be an unrestricted free agent with a $1.8 million cap hold and Non-Bird Rights. This means that the highest starting salary the Clippers could offer him using the Non-Bird Exception is $2.3 million.

Alternatively, the Clippers could use their $6.4 million Taxpayer Mid-Level Exception to re-sign Hartenstein if he demands more than $2.3 million. However, there's a chance that may not even be enough, especially considering Hartenstein is unlikely to take a discount to return to Los Angeles considering he has made relatively little money thus far in his career.

Other teams will have multiple ways to sign Hartenstein as even teams without cap space could possibly use the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE or Bi-Annual Exception to sign him.