Your question comes across (to me at least) somewhat similar to an XY problem. Having looked at the links in your post, it seems you've got a reason to use an outdoor charging device (hence the Solar Charger) and are looking at how you could get this to work.
There are actually products designed specifically to charge MacBooks and other laptops when people are on the go (e.g. backpacks with built-in solar chargers, etc) and a dedicated product is going to be a much more convenient and reliable charging source than the approach you're looking at here.
That said, to answer your question, some concerns around this approach are:
- this charger is not designed to charge laptops
- for this particular charger to work in your scenario you need multiple 3rd party items (i.e. an adapter cable and a USB-C to USB A connector)
- The long time it will take for this to charge your MacBook (which you've already noted)
In a nutshell:
- there is no disadvantage to the MacBook Pro itself
- there is likely to be a disadvantage for the solar charger - I suspect it will work, but its lifespan will be reduced. That said I see it has an 18 month warranty (although using it in this way may void that).
- there are disadvantages to you in that it will need to be switched off during charging and the fact charging will take long durations of time.
If it was me and I needed to charge a MacBook Pro on the go on a regular basis (not sure this is your situation), I would look at options such as those offered by Voltaic Systems.
If this is only something you need to do occasionally, (e.g. a couple of camping trips a year), then your approach will probably be fine, although not the best option.