I'm currently using the Retra snoot. Although I haven't used it a lot yet, I must say I really like it. I used a "normal" snoot before, but I like the Retra much more. Since I have a Retra, the normal snoot hasn't been used any more.
With a normal snoot, I had to open my aperture towards F11-F13 while shooting at full power, that much light was lost.
With the Retra, I can use apertures like I'm used to when I'm not using a snoot, the light loss is minimal. Because the light loss is far less then with a normal snoot, you can also see the focus light much better. This makes aiming your snoot a lot easier, specially during the daytimes.
As for the weight: this is mostly a "problem" out of the water, underwater the Retra is negative for sure, but not very much.
I never take my Retra off the Z240 underwater, when I want to take a picture without a snoot, I turn on my second strobe (also Z240)
good luck with your choise,