Thanks for the responses! It is clear that GL.inet does not officially support DD-WRT. It is also clear that there is a demand for DD-WRT and that external organizations and some customers imply that DD-WRT works on your hardware. I found a second review listing the GL-MT300N v2 as one of the best DD-WRT routers of 2018. This is probably a result of people not realizing the V2 uses a different chip set than the earlier model. So GL.inet does not publicize support of DD-WRT, but others suggest DD-wrt and then new customers brick their routers.

I was curious about OpenWRT, but wanted more DD-wrt routers for learning projects. Open-Wrt may be better, but as some reviews note that the version on the GL-2300N v2 router is dumbed-down. DD-wrt has better support in Google searches, but identifying supported routers and correct version of firmware is a challenge.

I would like learn more about DD-WRT, but one first tasks will be to compare features with Pfsense. Information about Open-wrt seems harder to find.

I am not critical of Open-wrt or GL-inet. I was just looking for a DD-wrt test router and bought two GL-MT300N routers by mistake. I would have bought more, but now wonder about ALL models of of GL,inet routers.