I'll chime in: I bought 2 from medtech spaced apart about 1yr, because the first one broke.
I'll say a few words about them: these are GREAT when taking an enema in bed, or for some really kinky water play (details futher down). When I used these, I had a custom automatic enema machine that was programmed with volume and max pressure. It would inject water until the max pressure is reached (e.g. cramps) then stop, then inject again until the total volume is reached. I had more than one orgasm this way. But safe it ain't.
However, for "normal" enemas, they aren't very helpful - and it's not very safe to prevent expulsion no matter what.
In time both catheters broke - I never used grease, but the rubber lost its elasticity and developed thin spots.
Nowadays, I use an inflatable enema plug that is silicone - I got it from AliExpress, wasn't happy with it and modified it (replaced the enema tube with one-piece silicone).
https://www.aliexpress.com/item/1005005269983121.html?spm=a2g0o.productlist.main.11.5ac15560Ag2Xa4&algo_pvid=1b8f4e71-cd15-4811-b143-2eeaefb0ba1c&algo_exp_id=1b8f4e71-cd15-4811-b143-2eeaefb0ba1c-10&pdp_ext_f=%7B%22order%22%3A%2294%22%2C%22spu_best_type%22%3A%22price%22%2C%22eval%22%3A%221%22%2C%22fromPage%22%3A%22search%22%7D&pdp_npi=6%40dis%21RON%2173.07%2163.66%21%21%2116.31%2114.21%21%40211b813b17728094838133814e748a%2112000032429439009%21sea%21RO%210%21ABX%211%210%21n_tag%3A-29910%3Bd%3Ae019d7ff%3Bm03_new_user%3A-29895%3BpisId%3A5000000201130828&curPageLogUid=1V9FOCsdW7ua&utparam-url=scene%3Asearch%7Cquery_from%3A
My opinion: DBCs are fun, quite kinky, but a bit involved and quite dear. Also prone to break (in my experience).
Beware of silicone dbcs from Ali - the balloons are too far apart and don't seal well.