Yes you need to risk assess the site regarding what grade system the site needs, but many people just go 'grade 2 that will do'
Grade 2 is cheaper than grade 3
bear in mind the honeywell galaxy g2 is a grade 2 (std wise) part
honeywell optima gen4 is grade 1 (in fact it may be 4737 id have to look)
honeywell dimension is Grade 3
Flex is both G2 and G3 depending on model and config