Well, Resiblock themselves can answer that on their website, but, to paraphrase....
1 - it's been developed especially for use on block pavements rather than a 'jack-of-all-trades' product like Water Seal.
2 - it's a SPPU rather than an acrylic
3 - it binds the jointing sand as well as seals the surface.
4 - it has been extensively tested in the most aggressive of conditions, including airport runways.
5 - it *should* have a lifespan greater than an acrylic, possibly twice as long or more.
6 - it comes in a variety of finishes including gloss, satin or matt, to use paint terminology.
7 - it's used by the trade for the trade, whereas Water Seal et al is more of a DIY solution.
Have a look at the Resiblock website