I think the products in Chris' links will pretty much be the same - just different brands.
I've used the "joint-it" on my patio a few years ago so I can vouch for that stuff. When it sets, it sets rock hard. Also, you don't need to use a paint brush to brush it in, you pour some of the bag out on to the patio and brush it in with a sweeping brush - much easier than getting down on your hands and knees :)
Also, another tip which isn't mentioned in the instructions, when I brushed the powder into the joints, rather than just let the powder find its own level, I compacted it down using a piece of wood which fit in between the joints and then added more powder and kept repeating until the level of the powder was level with the patio flags.
I don't know if it made any difference, but a few years later on and all the pointing is still in place, none of it has cracked, etc :)
Here's a link on Ebay, to the same seller that I used:
https://www.ebay.co.uk/itm/Joint-it-Easy-All-Weather-Paving-Jointing-Grout-Mortar-Compound-20Kg-3-Colours/252062289603?ssPageName=STRK%3AMEBIDX%3AIT&var=550917021514&_trksid=p2060353.m1438.l2649