Apologies for the length of this post, I wanted to be thorough.
I recently bought the
Juya High Performance Velcro Short Binder from Les Love Boat in size L. My overbust is 36", my underbust 32".
The ordering process was very easy. Shipping was prompt, they told me it would take 10 to 14 business days, but it arrived in 7.
According to the relevant size chart on the website, a size L for this binder fits overbusts from 34" - 36". I've been steadily losing weight over the past year so I thought this size would be perfect — fitting me now, and yet giving me some room to lose weight. My only worry was that, since I'm right at the upper end of the size range, it might be too small. Not so. It fits me well, however, it fits me well when I have the velcro done up as far as it will go. If I lose more weight, it could easily become too large. Thankfully I can sew, so I can take it in if need be, and it still fits me fine for now. With the binder on, the widest part of my chest measures 33".
Side-on comparison, sports bra vs. binder:


Excuse my cluttered bedroom.
Front view:

The front view isn't entirely representative, IMHO - the underboob shadows seen here make it look like it doesn't bind as well as it does. If you look at the side view you can see that the fabric continues down quite straight and hides the transition from breasts to midriff fairly well.
This binder is REALLY comfortable. I'd say it was about the same level of overall comfort as many of the sports bras I own. I've not tried Underworks binders but I have tried homemade binders made from similar spandex net, as well as one made with wide elastic similar to T-Kingdom. While they worked well, my chest felt quite constricted and there could be a lot of chafing, especially under the arms. This binder has no such problems. Rather than constricting, the pressure feels more comparable to a hug. It actually feels very "secure" and reassuring to me. My ability to breath deeply is barely hindered at all. I wouldn't say it's at 100%, but there's no real noticible difficulty.
One issue I have with this binder is that there are some problems with it not binding as well above the arm holes. It doesn't look too terrible but there are some lumps there, as you can see in the side view. Since the arm holes aren't cut that high on me, and there's a lot of slack in the upper part of the shoulder straps, I'm actually planning on taking it in along the shoulder seam. I've tried hitching it up by the shoulders to see how what difference it makes, and it seems like it will help a lot towards flattening out the lumps.
Like so:

According to the website, this binder is made from Tactel. Tactel is a trademarked brand of nylon, produced by Invista, much like Lycra is Invista's trademarked brand of elastane/spandex. The binder fabric feels pretty similar to other nylon microfibre/elastane mix fabrics that are frequently used for things like underwear — e.g. I have a piece of clothing that is 93% Meryl nylon, 7% spandex, and it feels identical to what the binder is made from. It's very smooth, almost slippery, and doesn't pill easily.
The front is two layers of Tactel with a non-stretch interlayer between them, and the back is one layer of Tactel. This non-stretch interlayer is fused to the inner layer of Tactel and then stitched on at regular intervals. I actually think it feels like fusible interfacing. It's not especially thick and doesn't add much bulk, and the non-stretch nature of the front really helps smooth out curves. The non-stretch interlayer ends at neckline level.
The velcro is pretty good. The side with the hooks feels a little sturdier and the hooks themselves are shorter than what I'm used to.
Front view of the binder alone, with the velcro undone:

Showing the velcro:

Back view, velcro fastened:

Wearing it under a t-shirt:


Under a shirt:


All in all, I'm very happy with it. I think it looks much better under a shirt than a t-shirt, but hopefully taking it in along the shoulder will reduce the lumpiness in the upper chest, and help this.