Solar charging ensures you only rarely have to plug it in to top it up, which is convenient. It also means that if you leave it sitting outside for long periods of time, it will be topped up rather than slightly drained when you get back to it. That convenience is not worth a lot of course but solar panels are cheap. And also, not having to pay for the electricity is nice.
E.g. my mother has a car that averages less than 3000 km/year (seriously). With this, she'd never have to plug it in (or rather visit a petrol station). My parents live in a small village and most of the trips are basically 15km round trips to a near by city. Something like this but a bit cheaper would be perfect for them and decimate their fuel expenses.
Will this cover all your needs? No of course not. But solar panels are cheap so the added cost of this convenience might be worth it.