My experience and what my customers tell me, with hundreds gas R/C engines and hundreds of spark plugs :

NGK CM6/Honda : good spark plug. Too expensive here.
Chinnese spark plugs :
I have tested at least 6 different CM6 clones. Most of them aren't reliable, and will last few time, but NOT all performs the same.

DL/DLE : don't last much time, many times fails in the break-in . Better to replace by a NGK or RCEXL before put the airplane on air.
RCEXL CM6 stainless steel top : same performance than NGK CM6 .
RCEXL ICM6 : very good performance, and when the engine is not well set on low needle, help to start. Not tested too much time yet, but i like this spark-plug, same price or less than geniune NGK CM6 here in my country.
I've mounted the stainless steel top RCEXL CM6 on most engines i repair and tested, and no one claims against this spark plug. Cheaper than NGK ...

Note :
On the CRRC bag, the CRRC CM6 spark.
From left :
The DLE CM6, JC CM6 , RCEXL stainless steel top, RCEXL ICM6, HONDA marked NGK CM6 , and the NGK CM6.

Regards