Re: Screen rather then foil?
Metal screens have no upsides other then not sagging which is not an issue as I almost always use the small funnel/scalli combo. Besides the problems already mentioned screens all have the same pattern and often different sorts of patterns are needed. As a result, i'd say don't bother with metal screens.
Pyrex screens and bowls are supposed to be very good but they are very expensive and given how often ceramic bowls brake i'm not to delighted with the prospect of wrecking a $30 bowl or a $6 screen. Besides, funnels are wonderful and cost about a third of what pyrex does so i'm not tempted to switch.