The positives make these far more enjoyable than any negatives we've found so far:

About the glass: it's medical grade, so don't be too concerned that it will break, (at least during regular play, I wouldn't toss it against the wall.) and is rated to 143 psi, which you won't get from these bulbs.

While certainly there are other products that will do the suction trick, I haven't found any with the added fun of the rubber rings, and oh! those are most definitely delectable! We tried this out the first time in the daylight, without the pressure of "oh my god if we don't do it right the first time it's totally ruined!" (makes things easier if there are variables involved: what size ring to use, stretching it over the end, seeing how the thing works: so much better to start with humor and not worry!) Yep, it actually worked perfectly the first time and was -quite- pleasurable for both me, the recipient, and him, the participant.

The different sizes of the rubber rings give a chance for not only variable nipple sizes, but also for variable levels of stimulation; it's certainly worth some experimenting!

While we've yet to fully give it a try on him, it seemed like it might work, even thought he's going to need to remove hair around his nipples to get full suction.

Overall, this is quite a fun item, and we're looking forward to several different uses (such as 'how long can we leave them on in public without losing my mind,' and other ridiculously great things). For us, leaving the bulb part on by itself isn't our thing, we'd likely use something else for that, but for the use of putting those rubber rings on (and perhaps sensation play on other places!), I like 'em, and he-of-the-Ruled-By-The-Visuals says that seeing the suction happening through the glass is 'hot'. I'm inclined to agree.

We found that one of the bulbs 'squashed up' on use, so looked -everywhere- how to make that not happen: what has helped is warming the bulb up a little and having a bit of moisture/lotion already on the nipple. I've seen "partially squeezing the bulb" recommended to help this issue, but it didn't seem to work for us.