I have very limited experience with scooters, and dating back almost 40 years, when I did build one, which did flood at the first dive....
So I cannot give you any serious advice on them.
But I am a finned-swimming instructor...
So I am wondering what is your husband's problem, making him "less able to kick well". I understand that answering to this question could mean disclosing something private regarding health or abilities of your husband, so if this makes you uncomfortable, please just ignore my post.
If instead you can provide more info, I think I can help pointing him to technical solutions and skills which will make him more than capable of "kicking well"...
Nowadays most diving instructors do not start, as me, as swimming instructors, then become finned swimming instructors, and then free diving instructors, and finally scuba diving instructors...
Having jumped over the first three steps of this ladder, makes them giving small relevance to proper swimming techniques, or breathing techniques, or hand propulsion techniques. And you see divers which are trained to very advanced technical topics, but who still have no proper control on their breathing or propulsion.
So I think that, before going with a scooter, we should try to bring your husband to the best propulsion capabilities using his muscles. And only when they do not suffice, he will need the help of electrical propulsion.