I really like the boards on my RSV/Hannigan.
In my opinion, a trike looks better with them. A trike without them looks incomplete to my eye. I know some disagree with this.
I you don't have a reverse you need to be careful how you park so you can coast out.
They help keep some, not all, of the road debris from hitting the rear fenders.
In rainy weather my feet and lower legs stay much, much drier.
The trike experience is much different than 2 wheels but a lot of fun.
Make sure whatever you are looking at has independent rear suspension. It makes a world of difference.