The seller was e4Hats (fulfilled by Amazon). I paid 20 bucks. The olive color is not as dark as it appears in the photo on amazon, but I don't care.  It still looks fine.

The hat appears to be well constructed even though it is made in China.  The draw string in the back goes about halfway around the inside of the hat on both sides, and is sewn into the inside brim of the hat with only one stitch on each side, so I wouldn't pull on it too hard if you are going to tighten it.  There is an elastic band around the back half of the hat, and that helps to make it "one size fits all".  For myself, I prefer a loose fitting hat (my head measures about 23" around just above my ears, making my hat size about 7-3/8"); the hat fits me just fine--not snug, but not too loose...I tightened the draw string just a little).  Your "fit" may also depend on how much hair you have on your head...in my case, not much!

The hat also includes a cord with a clamp, so you can clamp it to your shirt.  It appears that it also is sewn into the brim of the hat...probably with one stitch.  If a gust of wind blows off the hat, the clamp should keep it from blowing away.  So, you really don't need to tighten the hat with the draw string, unless it's a windy day (or the hat fits too loose on your head).

The vale/flap in the back is just the right length and position, and it shelters my ears a bit as well (it doesn't cover my ears, but it hangs just behind them...angling toward the back).

The bill of the hat is 3.5" and extends around the front of the hat from ear to ear.  It stops at the ear, and that's where the vale/flap starts.

It does have 2 mesh holes on both sides, and mesh around the base of the hat (as you can see from the photo).  However, the mesh at the base of the hat is mostly covered by the sweat band on the inside; so, I'm not sure how effective the air circulation will be (and it's not hot enough yet to test that part of it).

The tag on the inside of the hat says "Juniper" and has these markings:
7419/#7002A
100% polyester
one size fits all
RN 129231

The same hat comes in Khaki:&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/4-Panel-Large-Bill-Flap-Hat-W15S48B-One-Size-Fits-Most-Khaki/dp/B000PKT8SK/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">4 Panel Large Bill Flap Hat W15S48B (One Size Fits Most/Khaki)</a>.

Here are two more variations:&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Men-s-Khaki-Fishing-Boating-Sun-Flap-Wide-Bill-Hat-Cap/dp/B004TGFOH0/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Men's Khaki Fishing Boating Sun Flap Wide Bill Hat Cap</a>, and&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Men-s-Olive-Fishing-Boating-Sun-Flap-Wide-Bill-Hat-Cap/dp/B004TGAYGQ/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Men's Olive Fishing Boating Sun Flap Wide Bill Hat Cap</a>.

There is another variation of this hat that has a zippered pocket in the flap that covers your neck:&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Extreme-Condition-Sun-Hat-STONE/dp/B000QCJS0U/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Extreme Condition Sun Hat STONE</a>. And here is another variation (<a data-hook="product-link-linked" class="a-link-normal" href="/ADAM-S-HEADWEAR-EXTREME-CONDITION-HAT-UPF-45-6-Colors/dp/B007ZH3EF4/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">ADAM'S HEADWEAR EXTREME CONDITION HAT - UPF 45+ - 6 Colors</a>), but one reviewer said there was no zipper.

UPDATE 5/25/12
I used this hat while visiting some theme parks in Florida.  It's easy to pack.  It worked very well.  During rides, I easily tucked the hat into the front of my shirt, so that it would not fly away.  The cord/clamp worked well (I secured it to my shirt for the occasional gust of wind); I did not have to remove the clamp when tucking the hat into my shirt.  The weather was in the 80s; I did not think the hat was "hot"; the hat construction is thin (except for the bill), and that may help to keep it cool (it may also help that I had a crew cut).  I am pleased with my purchase.

UPDATE 3/11/16
I tried to order another hat. The seller was Gravity Trading. They sent me a hat that has a limp brim, no cord/clamp, and has F-006 on the label (made in China). The hat felt cheap and was poorly made (it was unfinished on the inside), as compared to the original hat that I ordered in 2012. I requested a pre-paid return, since the item does not match the Amazon description. They sent me the correct hat, and provided a pre-paid return label for the wrong hat.

The seller that I originally bought the hat from is still listed as a seller on Amazon for this item. I called e4Hats, but they had no way to confirm that the hat they are selling today is the same as the one I purchased in 2012. So, I will look elsewhere.