I dot not like cylinder shells for two reasons:
1. It is impossible to obtain a symmetrical aperture;
2. The cylinder shape obliges to use a star plate instead a star roller.
For the second reason, using metals like titanium of a particular mesh will grip the pistons of the star plate inside its cylinders
and everything will finish into a big mess.
The biggest firework in the world was a rounded japanese 48" shell and not a 48" cylinder shell.
The multibreak will be obtained also with a traditional rounded shell playing a lot with the delays.
It is not impossible to get a symmetrical break with a cylinder shell, it just depends on the orientation of the shell to the viewer which, unless the shell is mounted as a header on a rocket, is largely at random.
It is also not required to use pumped stars in a cylinder shell. Single break shells can, and are, easily made using cut stars, or even rolled stars if you prefer. When building multibreaks pumped comets are generally necessary to provide structural integrity, but then it's something of a moot point because how many guys are building multi-break ball shells? I know people do build peanut shells, but cylinder shells are far more conducive to multi-break construction. Also, there are solutions to problem of pumping stars with hard metals: use a small layer of comp without metal or chipboard disks. Yes, it's more work, but it can be done.
As for the biggest shell. 1. So what? 2. Comparing ball and cylinder shells based simply on diameter is somewhat misleading. The volume of a cylinder is 1/3 greater than a sphere of the same diameter. That aside, many Italian and Maltese multi-breaks are as long or longer than the guns they're fired from. I've personally made a 4" multibreak that was over 22" tall. A 4" ball shell is...4" tall.
I like ball shells, and admire the skill it takes to get a perfectly round break, or a well time color change, but man do I love those big multi-break logs.