Good lord, some cheap or thin glass these things have. I don't even tighten it down crazy hard and for no reason in 4 weeks broke both glass sections, juse in travel...this is ridiculous. Its my backup daily driver so i don't use it but so much but Im really let down with this RTA. Do they have a metal tank? China post can't come fast enough now.
Well its really not that thin, as a matter of fact its pretty much average with 1.5mm walls, which is fairly common. Quality of the glass is average, not Boro tough, but not plain glass cheap either, my guess would be a lower grade more commonly used in China Pyrex.
It is not a common complaint for the Merlin, so evidence would point to another issue, over-tightening would be a first guess, which would put undue stress on the tank, and could cause failure over time. Also a manufacturing defect is possible, but more difficult to prove without a good digital caliper and thorough inspection.
My personal experience is that the glass seems to be fairly robust. I've not dropped mine but I've played mod-domino more then once with it, and had it fall over with the full weight of larger a mod onto another atty. While a steel tank or maybe thicker 2mm walls may be helpful I think it may end up causing issues with the press fit deck especially in rougher environments.
After this long winded response the bottom line is the Merlin glass is not the more expensive and rugged Boro/quartz tubes, however unless they are mishandled they should not be breaking as your experiencing.
I would try making a conscious effort to not tighten them so much. I would also check for any metal to glass contact due to a manufacturing defect. I would also make certain the o-rings sealing the tank ends do not seem overly tight.
You could hit up IBtanked, or Bedazzled for some high quality Quartz replacements, but that may not be the best solution. Perhaps you might be just better off with one of the steel tanked atomizers currently available.