my personal opinion is that Gready, defi, blitz....are all overpriced and not sure on the quality... (not bagging AJPS or anyone that sells/stocks them)
i never buy anything other than VDO
my dad is a marine electrician and has been buying and installing these gauges for like last 10years, and hasn't had a problem (i get a trade discount too!)
the quality of VDO is excellent, they have PROPER catalogues of all their guages AND senders, with lots of information for picking the right one.
anddd you can buy them from repco etc, just have to make sure the dude behind the counter can read numbers....