if you were going by yourself on a bike ride, would you choose a bicycle built for two ?

solo canoes are designed and built for a reason - they are better to solo in than a tandem - if that weren't so, no one would be buying them and with no market, no one would make them

a reasonable measure of efficiency is the length to width ratio - given a tandem and solo of the same length, the narrower solo will be a more efficient/faster boat; being lighter, it shoudl take less work to move thru the water than a heavier tandem, and being narrower, its easier to get a vertical forward stroke in the solo

as mentioned, they will seem to be less stable, due to the narrower width, but that is easily gotten used to.  best thing you can do for the first time you get into a solo boat is to just sit in it near shore and rock it side to side - keep you torso upright/perpenducular to the lake, and rock at the hips - after a few of minutes of that, you will gain confidence and kind of an instinct for keeping the torso upright - just don't lean the torso off to the sides unless you really want to heel the boat.  With a load of gear sinking the boat deeper, it will automatically become more stable than when empty, and if you trim for it (sternheavy) you can kneel to increase stability, though that's not easy to do if you get a boat wiht a tractor seat - better with a bench seat

there is also a learning curve as to paddling the solo boat - you can use a sit n' switch method -i.e. 3 or 4 stroks on the right, then switch to left and give it another 3 or 4 strokes, averaging out the yaw - essentially eliminating "steering" once your pointed in the right direction -
I prefer to use the "C" stroke which is a constant correcton/steering stroke - either will work.  A boat like the Prism or Magic is designed to go straight more than it is designed to turn, and are a better choice for sit n' switch than the Merlin, which is more the opposite and a bit harder to keep going straigt at first.  - if you just do a forward stroke and J every time, you are working against yourself, robbing yourself of the forward momentum.  Go to your library and see what books (and vidoes) they may have on canoeing - you can find lots of instructional type stuff in YouTube as well.  Learning a draw and sweep stroke will help in turning a lot.

most experienced paddlers shouldn't have much trouble adjusting to a solo boat if you take a bit of time to learn it

one critical element of tripping with a solo is to properly trim the boat - you sit just back of center, and its best to have two packs - a heavier one behind, and a lighter (or at least no heavier) pack toward the bow - I tie a short length of rope to the bag in the bow, so I can pull it back towards me, and I can push it forward with my paddle - trim a little bit bow heavy for headwind, and a little sterrn heavy for taiwind - you will be adjusting a lot as you go along - no big deal

on the other hand, you can use a tandem and reverse it and paddle from the bow seat facing the stern, and load all your gear up near the bow - it won't turn as easily as a solo, nor be as easy to control in the wind, nor be as efficient, but it will be more stable, and track a bit better unless its windy - its never windy there, is it?.

if you own a lightweight tandem, it might well be better to use it than to rent a solo, but renting a solo will give you an opportunity to try something different

I've paddled tandems a few time solo, never tripping with one - I just wouldn't want to, but maybe that's just me