I've got a ZR+120 (without volumetric alarm again) but have to say, doesn't overly bother me.
Before buying my Zed, I looked round at a few other marques and I was amazed how many of them no longer include alarms at all on new models. I think one of the new Citroens (don't ask why I was looking at them!) doesn't come with an alarm and as the salesperson said "when you hear an alarm ringing, what do you do?". Point made.
I think the best thing is to say to yourself: look, it's got a basic alarm but it's also got an immobiliser. Regardless of any after market alarm, a determined thief will probably get the car anyway regardless. If you wanna stop em breaking in, to start with, no alarm whatsoever will do that. Park in well lit areas, ideally close to busy spots and cross your fingers!
Save the money you were gonna spend on car and get some mods!