I've tried nimh in some TV Remotes and they don't work as well / far of range as w/ alkalines. I think the voltage drop made the difference. Alkalines last near forever in my remotes so it's a non-issue to me.
The nimh's work well in 99% of childrens toys. A few had problems, but just until I switched to alkaline. Thus, so far so good. Virtually no risk--although in theory some things will draw too much current if the voltage is dropped... (in order to keep the watts the same) if you think the device (you try them in) is running warmer than before you might want to go back to alkaline.