subwoofer box build

A 28" squared subwoofer landed(allegedly does single digits to 600hz linear<unknown SPL>). As it happens it's very shallow which makes it very appealing for some people (like me) so I have to ask: What's the catch? Why nobody else thought to build shallow subs like this? How does this compare...

I'm not sure if I'm wording this correctly... I'm building a box for my manager for his two ds18 exl 12inch 2500watt subs... I've tried googling it, but I can't find any info for using a port in between two subwoofers in a 'parallel isobaric load'? If thats the correct technical definition? I'm...