There are many brands of both tadpole & delta style trikes these days.
I have 2 tried & true Greenspeeds. Wonderful, simple, rugged designs.
From my experience, I would recommend a Greenspeed GTO or GTR.
The 20" wheels are pretty standard stuff & tough. And the ground clearance is good too.
A friend of mine has a GTR that has the Rholoff 14 speed hub and the Schlumph speed drive.
28 speeds & no deraileurs to go wrong.
If budget is a factor (Greenspeeds new, aren't "entry level" rigs) definetly look for used.
You may end up paying close to retail, but you don't have the wait associated with ordering "your own" brand new rig. Or you may find a deal and save a bundle.
(I just sold an ICE X2 for $6K! A DEAL??? new....$14,682.00! So, YES! Stinking good deal!!!
But it still cost $6K!
And if you are anywhere near here, PM me, and I'll let you & your friend try mine!