check if it’s reliable in long run or I would get no-free-ch or denied messages
The “no-free-ch” is a normal response, so please don’t take it as a sign of an issue or lack of interop between systems. It is purely a duty-cycle safe guard as described in the LoRaWAN spec.
I.e. if you get “no-free-ch” as a response, you are exceeding the duty cycle restrictions of the spectrum.
Defaults are 3 channels each with 0.33% duty-cycle allocated.
You can disable this (as during during certification testing) or over-ride the limit with a higher value, but it should be done consciously and in accordance with regional limits.
The “denied” response during OTAA join is similar, but note that join has its own duty-cycle limit of 0.1%, again, from the LoRaWAN spec. So you get 3 chances (3 default channels) then have to wait.
Also note that the response “denied” is given due to no response from the server, again from the LoRaWAN spec. So from the response at the command line, its not possible to say if the server really denied the join, or just didn’t response, didn’t hear the request, or just had a poor channel in the downlink.