Ooh, that's just there to confuse you even more! See the
sub in that description? That's their new subohm tank that uses a factory 0.2 ohm notch coil, not a rebuildable deck. And it's a 5 ml tank, not 3.5 ml. Here it is at MVS
http://www.myvaporstore.com/OBS-Engine-SUB-p/obs-eng20.htm
Somehow that GearBest thing is a mashup of different tanks. Note how they mention it comes with a 0.2 ohm coil.
Personally, I'd love a 23 mm 3.5 ml single coil deck Engine. But as mini and nano are now taken, I guess maybe micro for that version?
Top airflow is something you will see a lot more of. It's primarily being designed with upcoming EU TPD regulations in mind which will not only place restrictions on tank volume (2 ml max) but also carries anti-leak requirements. Building with top airflow is a reasonable way of meeting those requirements and is already seen in several other tanks on the market. So it's not really a step backward, but rather a step towards remaining complaint and available for sale in the EU (at least for now).
Obviously in the case of the Engine, the volume exceeds TPD specs, but the tech will help assure future designs will perform acceptably. In the case of the Engine, IMHO, I think they pulled off a great job at making top airflow perform well while offering the inherent anti-leak benefits of the design. As you say, we all have to find what works best for each of us.
Edit: What
@Roadtrip635 said about the subohm tank while I was typing away in between bites of my dinner.