Starting off, these straps are a bit hard to describe which might be one reason why they are harder to find. Sometimes called straps, cuffs, or belts they also mix up further descriptions such as suspension, tension, and hanging. I'd say suspension is the most confusing, to me at least, as it infers full body weight suspension. A lot of products seem to use the word suspension freely on that note, and likely a term like partial suspension would be better. 

Narrowing it down, I think Leather Tension straps best describe what they are since not quite cuffs or buckles and don't necessarily have to be used for suspension or hanging. Anyway, names aside I think they are quite handy for securing limbs with quick placement and removal functionality. The basic idea is a leather strap where one end is a loop and the strap goes through the loop to create a cinch effect. Thus the tighter one pulls, the tighter the cinch becomes making them work very well at preventing limbs slipping out. As a great plus, on a bound hand the extension of the strap makes for a great grabbing point for the bottom to allow offloading of some weight and tension. The natural friction of the leather makes the cinch generally stay in place so fully loosening becomes a 2 hand operation. Just a little tension makes them near impossible for a sassy sub to get out of them with just the bound hand so they end up being a lot more secure than they first appear. Since no buckles or locks are needed I love the speed they can be slipped on and secured along with fairly low hassle when it comes time to finally take them off.

The first pair I got was from BONBDSM which were are really heavy duty built, even using screws instead of rivets, however even after trying to break them in they are still a bit stiff so can make for pressure points on the wrists. BONBDSM appears to be male centric company so it may just be a boys sure play rough kind of thing. Still liking the general strap concept I tried another version that looked softer, being the DOMINIX Deluxe Leather Hanging Straps from LoveHoney. Construction wise these don't look quite as mega durable, but they are much softer with great padding on the edges. Kate was much happier with the DOMINIX straps on her wrists and fortunately the BONBDSM straps still work out great on her ankles. As shown in my pictures the straps function well for hands above head, spread eagle, and anything similar. I've even had luck wrapping them around her waist with hands behind back to create a more cuff like result.

Sadly the DOMINIX ones appear discontinued so the best I can recommend is looking for versions that are soft and or with lots of padding, the edges being the most important. I'm spreading the word as I totally wish I knew about these handy straps earlier in my BDSM adventures.

Places to purchase:
NL Leather appears to show pictures showing the nicely padded ones (possibly made the DOMINIX series), but it is unclear where to buy http://www.nlleather.com/en/shop/Suspension/Suspension_Wrist_Cuffs.html
BONBDSM https://www.etsy.com/shop/BONBDSM?ref=l2-shopheader-name and http://bonbdsm.com/

Additional ones I was able to find, but have not tried in person:
WithPleasureLeather https://www.etsy.com/listing/249858673/leather-suspension-handcuffs-angel?ref=shop_home_active_15
Eurotique http://www.eurotique.com/tensionsuspensionwristcuffs.aspx
(Appears to be made by KOOKIE INTL http://www.kookieintl.com/Merchant5/merchant.mvc?Screen=PROD&Store_Code=KI&Product_Code=3410&Category_Code=Suspension )
Fantasy Leather http://www.fantasyleather.co.uk/acatalog/Suspension.html