Suggestion for CTD, Ph sensors


Hi everyone,
I’m planning to use Ctd and ph sensor for Openrov.( I wont use to openrov hardware and software. It will be external)
I found many sensor about it but their prices are so high but finally i found two sensor brand. Their prices are acceptable.
First Brand is atlas scientific : Prices are about $200 for each.
Second Brand is Global Water : Prices are about $800 for each.

I can not make comparison between them. Why their prices are so different ? Are they laboratory equipment ? Are they suitable for using with OpenRov ?
Anyone have a knowledge about it ?