I can't say whether this silver protection shield is any better than the "lower" quality alternatives, because I don't have the experience of them all, but I can say that it looks good, was very easy to mould to shape, and has fitted comfortably and reliably for the last month since purchase.
You simply heat in hot water, and bite down to mould to a snug fit. As plastic cools it takes a permanent shape to fit your particular set of teeth.
If you get it wrong (hard to get wrong, but possible I suppose), then you simply reheat and remould.