G'day Kip,

Liners cannot be tested for a temperature rating, there's just not enough to them for current testing methods to be effective at all.  What this means is that a brand can put whatever number they like on their liners, generally the more high-end or higher technicality brands have more of a rational behind the number.
Basically all of these liners will perform similarly, but wether or not that will translate to 10dgrees in real life for you is another question.  Out of all the liner choices. fleece will obviously be the warmest option.
The main difference with the Sea to Summit liner is that it uses a higher quality fleece which allows it to be warm but also has a smaller pack size and weight.  This is an advantage if you have to carry your camping gear around, or if you may use it for multiday hiking at any stage.

G'day Bec,

Its not better or worse, it's just different.
The Coleman fleece liner is designed for general campers and swaggers and will go into your standard rectangular sleeping bag.
Sea to Summit is more of a technical light weight adventuring company, so their gear is designed more with that in mine.  It's tapered to fit into Mummu or tapered-shaped bags, and is made from a more technical grade polar fleece meaning it's thinner, without compromising warmth and comfort, and lighter incase in needs to be carried.

Both are great options but for different reasons.  You could 100% use the Sea to Summit liner in either circumstance, but the Coleman one would be best for just camping.

Hope that helps.

G'day Barry,

Liners cant actually be tested for an insulative value, so any claims they have for a warmth rating need to be taken with a grain of salt.  I'm not aware of any liner that would turn a -5 bag into a -10 or -12 bag.  It's just not possible.
A liner will help to add extra warmth, and a fleece liner would do the trick, but not the the degree that it sounds like you are needing.
Theres a range of factors that go into sleeping warm, and the main ones that have the biggest imapact are the sleeping mat and the sleeping bag.
If you want to let us know what your current sleeping mat and bag model is, we can go from there and see how to get you sleeping warmer.