We faced this issue with my son (now 22). He has Downs and Autism, we need the chair only for trips like WDW, zoo, Six Flags, museums.
After the Maclaren, we used a companion chair for a few years. It was much lighter than a regular wheelchair, and we did not want him self propelling anyway. (it does not have the large wheels like a wheelchair, and it fairly cheap). One problem with it was that he would tend to hunch forward on it, which meant his posture was awful, and he missed out on looking around while being pushed.
We ended up with a Convaid chair, because what I really wanted was an adult type stroller, with him sitting at an angle. Much more comfortable, he can put his head back, and it is just about impossible for him to hunch. The foot rests swing to the side, and do not have to be removed, which is great too. He flips them to the side, and can climb out of it, and also gets back in and puts the foot rests back into position himself.
His chair is the Scout Transport model, it is really a Cadillac of a chair, way more then he needs to be honest. His came with a headrest extension, which he does use, but we don't even belt him in, there is no need. His is bright red. I got it on EBAY! I was SO lucky, it was never used, a family had another one that they used. This one was not needed, their daughter had to be placed in a facility (sadly). they are very expensive, I think I paid $1000, but it costs over $3000? (the transport model is more $$, but we did not really need this model, but it was a good deal). I considered it an investment, he can use it for decades, it holds up to 250 pounds. It is their largest model, 18". And it can be repaired if necessary. I think it is for 14 years and up, but they have smaller ones of course.
The only issue with Sean's chair is that it is HEAVY. And does not collapse into a small size, it does fold up, but it is still large. IF I was buying it new, not on Ebay, I would have went for a cheaper model most likely.