I'd go for the more expensive one, probably a better quality part. Trust me when I say, you do NOW want to do this job again

Oh, and get 2 new heater matrix feed & return pipes, as you no longer need the bypass valves:
18004 HEATER HOSE (FEED) 9.45
18005 HEATER HOSE (RETURN) 9.45
Or you could use lengths of copper pipe, but if you're doing a job... etc
