Jumping in - my husband uses a power chair full time because of MS. When we have cruised in the past, we have taken a manual chair as well, since this allowed us to go into ports, take cabs (he could transfer) etc. I LOVED having the manual chair. It was basically a luggage cart I was allowed to keep all the way to the gate, in line at port, etc.
Rather than considering a separate manual chair an inconvenience, you may find it is a Godsend.
My husband can no longer transfer, so we will not be taking the manual chair on our upcoming cruises, and I will miss it!