Sealing gaps in concrete drive

[Colh107]

My drive is ~50's concrete slabs. There's cracks in some, as well as the gaps between them - typically 3-5mm wide, which weeds of course love.
I guess a flexible sealant would be best, but is there any particular type/feature to look for amongst the myriad of products around?

 

[Wayners]

Epoxy concrete repair maybe. Never used it but see it advertised