Good topic. Just to see for myself I bought one each of the Twin Air, Uni, and an Outerwears. I made an admittedly unscientific examination of the two filter elements and I'll tell you what I found:
First I'll admit a personal bias toward the Twin Air, based on my satisfaction with one of them on my King Quad, a quad known at the beginning of their present model run for having an unsatisfactory factory air cleaner element. (sound familiar?)
Pics are in the following posts. Couldn't get all to load.
To the filters. Here they are brand new.
A filter that gets dirty like this had better be extraordinary.
I hold the filter elements to the light in turn (dry), and shoot a cell phone cam pic through the inlet hole. The first pic through the Uni is just black. Same as what I see. Nothing. No point wasting bandwidth on the pic, just imagine black.
Second is the inside of the Uni using the flash. This shows the form spring and the colour of the inside.
Now the Twin Air, without the flash. Don't need flash, enough light comes in for a good photo without flash. A lot of light is coming through the end of this filter, right through the foam but to my astonishment what the photo does not capture here is that the end cap is admitting pinpricks of unimpeded light! Dozens of tiny 'stars' of raw light are visible right through the foam. This is no exaggeration. The foam on the sides does it too, admits pinpricks of unimpeded light.
The resolution of the pic does not permit showing this and each tiny light source is lost in a pixel, but they were easy to see.
Does this rather crude review using un-oiled filter elements prove anything? Not really, I'm sure because a proper test would involve making the respective filter elements do what they are intended to do, in the condition they were intended to be, properly oiled and mounted on a test bed, flowing air and being measured for flow and actual filtering performance when exposed to equal parts contaminants.
But for a seat of the pants comparison there simply IS no comparison. The filter foam elements of the UNI are separate, one gloved over the other. The two together are at least 5/8" thick. The Twin Air are bonded together and total maybe 3/8", and that's being generous. The Uni feels sturdy and solid. The Twin Air feels flimsy and looks shabby with glue lines all over and an irregular shape. While I don't know if the Twin Air with no internal cage would actually collapse if badly dust coated and intake negative pressure was high, you don't have to wonder with the Uni, it has a spring inside to keep its shape regardless.
And those pinpricks of raw light. I still shake my head.
The Outerwears looks well made. I can't notice it at all with me breathing through just a small part of it, and there's lots of it. Enough people have stated that most times all they need to do is clean off the Outerwears and the rest of the filter looks good, that I believe them.
And it fits so nicely right over top the Uni.
Call me converted. I once assumed the Uni was a cheaper alternate to a good Twin Air (see, I never mentioned that it's cheaper to buy too. I always figured the air cleaner isn't where I want to economize), now I'm not so sure. I mean even the hose clamp on the Uni looks more rugged than the one on the Twin Air!
That's it. I'm not drinking the Twin Air Kool-Aid anymore.
