In principle this WILL work but there are a couple of things to consider first:
- This technique makes use of the felting properties of wool, so it will ONLY work if you are using wool or some other animal fibers (like alpaca). Furthermore, it needs to be untreated (anything that is labeled "superwash" or "machine washable" in generally is not going to work). This goes for BOTH the original sweater and the roving used for the repair. You know how the armpits of wool sweaters get kind of matted and firm after you wear them for a while? That's felting and is caused by agitation and/or moisture, and that is exactly what you are doing here.
-In the example, they've used a heathered sweater with a kind of rustic look, so the finished repair does not show. However, this is not a very delicate technique and on a finer, more solid colored piece, I think it WILL show. (The felted part will have no stitch definition.)
-Needle felting tool and roving are not something most people have laying around! (I am a knitter and I don't have them.) This will likely not work with most regular yarn (like what some sweaters come with for repairs) as roving is unspun and unstructured.
I would instead go for a darning technique like this:
http://blog.craftzine.com/arch.....rn_it.html
or this:
http://knitty.com/ISSUEspring0.....rs101.html
