The MRF-100 will accept RF from any URC RF remote, since the address is "open". This is why you can't use more than one, unless you are controlling completely different equipment with mutiple MRFs.
The MX-600 has a better LCD, IMO. The softkeys for the LCD help navigate by feel, rather than the URC-300 which you need to look at or the URC-200, which only has a single column of LCD buttons.
Thank you,
Damon DG
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