Dick,
The thing about anything that you plug and unplug outdoors, the plugs and contacts wear over time and the unit is exposed to weather. The 50 amp service plug we have now, the receptacle lives under a cover in most power panels out of the weather. My guess is this unit will not and will hang below the cover. On top of that it is visible and there are theft issues. On the good side if you may be changing coaches in the not too distant future this unit is portable. On balance I like the internal hardwired units best.
One could conceive of a third option, to add a 50 amp female and male receptacle in the incoming power feed line in the bay, such that they are pluggable to each other. Then you could add the portable unit out of the way and out of the weather. If you change coaches it could go with you and no theft issues. If it failed it would be an easy plug and change option.
This option could be installed in the line after the transfer switch so both the generator and outside power feed is protected. I had an instance on this last trip where a wire came loose in the generator terminal block that ties the coach and generator together. It was a hot wire so I lost 1/2 of the 120V feed while it was running. Had that been the neutral wire I would have had the dreaded open neutral line issue. The generators vibrate and this is a screw terminal block that was not of the best quality I have seen. If you are going to the trouble of hard wire and you can protect the coach from all power feed sources then that would be best. I'm not completely sure if you lost the neutral while in operation if any of these units would protect the coach. It goes through a pre-check and then connects, you are already connected when the neutral is lost and there is the sense and disconnect time. Power spikes are different, they get clamped as they rise and shorted to ground in milliseconds. Hope this helps.
Later Ed