Check out this review to see how the kits are packaged, instructions, etc:https://reefbase.co.uk/colombo/review-of-colombo-nitrate-and-phosphate-test-kits/
As a recap, they're very user friendly, and easy to use. The Calcium, Alkalinity, and Magnesium kits are very similar to the Salifert kits. The colours of the liquids are different, but just as easy to see neutralization point of the titration.
I thought I'd compare the values I got from these with my tried and trusted Salifert kits. These are the values I got:
Test | Colombo result | Salifert result
Kh | 5.8 | 5.7
Ca | 360 | 350
Mg | 1350 | 1200 (Salifert kit went out of date in Nov'16)
Ignoring that my Kh and Ca are low, the results are very similar. I'd put differences down to well within user error margins, so I'm very happy to trust the Colombo test kits for these two.
For Mg, my Salifert test kit is slightly out of date, and given that Mg normally doesn't deplete (I've no reason to think it would in my tank), I'm inclined to go with the Colombo result, which is spot on where I'd want Magnesium.
I've not dosed anything to my tank since setting it up in April, so I expected levels to be low (although not that low, as I don't have that many hard corals really). I've also bought a doser, so going to get that set up and sort my levels out.