Pros:
Unfortunately none. It was cheap so I was not expecting much anyway.
Cons:
a) Quality is not good. Very light and very small.
b) The curve of the metal slide itself is so tight it does not fit around my large fingers. It just digs into my finger like a staple instead. The adjustable strap fits around my finger but is pointless as the metal doesn't.
c) The slide surface is tiny, very hard to do anything useful with the area except play one string (or maybe at a push two). Requires very accurate positioning and pressure to avoid buzz with two or more strings. Especially as it is so light.
d) The velcro strip has the rough side left against your finger. A minor point but constant movement eventually makes your finger sore from the rubbing. This may not be the case if your hands are small enough to for inside the metal part but I suspect it will be the same.