You need to decide what you need to carry with you. There's no point looking for a 'small' saddle bag and then finding you want to carry 2 tubes with you and not being able to fit them in (like I did to start with)!
The Specialized bag is only slightly smaller size to the
Topeak Medium I'm using (& costs more!). My topeak has ~1L capacity and that's more than enough for 2 inner tubes along with a huge amount of other stuff (check back a few pages for the comments and a picture

). It also has an expansion zip for another 0.3L, I've not used it but if I wanted to carry arm/knee warmers and some food it has that option. The 'loop' on the back is handy to fit a light on with a clip, not many bags have these! There is also
smaller version of the Topeak Aero. The Topeak are one of the cheapest and well made (+well regarded!) ranges of saddlebag.
I did originally start with an
Ortleib Micro. Great bag, good clip on/off made it very quick to mount/remove and the roll top (ie no zips) was a nice option. Just not big enough for 2 tubes and tools! You might get 2 tubes in it and a small multitool but nothing else. Felt very waterproof, but I've never had a problem with water in my Topeak the last 18 months...