yeah..
personally (and please keep in mind, that we really talk about personal preference here

)
I like the Dingo (i.e. KARTS) much better than mini buggies (which the Talon is really)
IDK if your grandson wants to have someone else in the kart at all
someone that he needs to take care of at least or maybe even should listen to..
that's the exact opposite of driving a kart.
And while he could take a ride on his own in a two seater of course.. chances are (depending on number of siblings or friends, and most importantly the ability of his parents to let him ride alone) he can't as easily.
IDK.. I cannot tell what your grandkid is after, what his parents are like...
not even what Dingo you are actually talking about (that name was given to half a dozen different Manco karts even some two seaters)
Sooo
my advice would be to investigate your grandkids wishes.
let him point you to a kart he likes (maybe he likes two seaters.. maybe he wants full suspension... IDK)
And once the general layout is settled (1 or 2 seats, with or without suspension)
you can make a better decision.
I don't like the gy6es too much, not because the engine itself is bad or anything,
but none is the real deal (which in fact would be a Honda scooter engine)
All a chinese clones of that.
No two are identical for some odd reason.
So while some parts are more or less universal amongst gy6es; some are not!
And that's where the hassle begins.. especially when it comes to it's CVT
there are several different splined shafts around to fit the driver and driven to, more when it comes to the PTO shaft on the rear.. and if it has a Forward Reverse gearbox
you will have an even harder time finding replacement parts that fit.
The inferior design of the good old flathead B&S is beutifully simple..
can't find replacement parts.. slap on a predator and be done..
less power, less speed compared to a gy6 all true..
but it's sooo easy to maintain and repair
Now that being said:
both karts are for all I know good quality karts
(okay.. I'd call one a buggy rather than a kart but no less a good quality buggy

)
And whatever option you choose you did nothing wrong.
I prefere the simpler and cheaper and easier to maintain Dingo personally.
but that should not mean a thing to you or your grandkid
'sid