What is your level of experience, and what footwear do you already have? I tend to think of Timberland as having a premium for the name, and mostly as a fashion statement. Looking at their website, their Hutchinsion boot (for example) looks reasonable, but there are other leather boots that probably give you similar or better performance (however you define** it) for less money.
I'd want to be confident of my navigation before I went to the Brecon Beacons in the winter.
One word of warning - I really wouldn't go for a Timberland high boot (or any other high boot) for general hillwalking. High-leg boots can be very uncomfortable around the instep. Blisters there are not fun.
Unlike Sussamb, I have gone back to leather boots for when I want water resistance (otherwise I wear lightweight fell shoes with no liner - Innov8 Rocklite fell shoes fit my foot), but I think we'd probably both agree that fit for your foot is key, and I'm guessing that we'd both suggest that generally, lighter boots are more comfortable at the end of the day - I'm probably going for slightly heavier boots than they are - but a lot of my walking is in the Peak District, and with a lot of boggy peat, so the options are to try to keep the water out (or at least to limit it and let it warm if it gets in - leather boot for me) or accept feet that get wet, and go for something that drys quickly (fell shoes with good grip and no waterproof liner). For my walking, trail shoes with a waterproof liner aren't too good, as water gets in the top of the low shoe and stays in.
*I don't know about in the US
**Waterproofness, weight, grip, druability, breathability (some of these are contradictory).