They’re sort of bland by themselves, maybe a bit like hard cooked muscles. I’ve ordered them numerous times and had a favorite little french place run by Vietnamese that did them exquisitely with butter, garlic, white wine and lavender (save for the lavender, butter/garlic and butter/garlic/wine sauce is very common). Just about every time I order them I think of that place, some seriously good memories. Here’s a nutrition link (http://www.nutritiondata.com/facts/finfish-and-shellfish-products/7742/2) just remember cooking them changes it a bit and drowning them in butter isn’t doing any favors for your body, though it sure tastes good! They are usually fairly pricey ($8–15 for 6 but I’ve seen $24 for 8 which I thought was over priced considering the standard preparation) but I suspect that depends on the restaurant, location, and availability. They’re easy to prepare and easy to over cook, I’ve done it a couple times when I’ve been able to find them fresh (don’t know about the canned ones), if you can bake squid without it becoming rubbery you should be able to handle snails. They’re also good in pasta, I’ve done them with olive oil, red pepper, and grey salt over home made linguini which was great and had them in red sauce before which was good but the tomato seemed to over power them.
Give them a try! They’re really pretty easy to eat compared to some other “acquired tastes” but make sure you go to a restaurant you like/trust for the first time lest you get a poor quality serving.