First of all, there is a feel-good factor just in having this plectrum set. The presentation box is both visually pleasing and very practical. The wool felt material will shed fibers over time if subjected to abrasion, so keeping felt picks in your pocket or loosely tossed in your kit bag is not ideal.
I'm new to uke (although I've been strumming guitars for a long time), so it's nice to know that I have the full spectrum covered, from flimsy to stiff. There is a significant difference across the four in the grade/density of the fibres, as well as in the thickness and perhaps whatever bonding/stiffening agent is used.
The correlation between colour tone and stiffness is good design, bringing tactile feel/responsiveness, looks, and sound/attack together. Of course, this is also very practical: you can select the one you need at a glance when performing.
The box (or "tin") appears to be made of aluminium. It's both light and strong enough for the job. The one I received is slightly larger than the one pictured: mine fits three plectra across (angled snugly), leaving room for five more felt picks or many more guitar picks. There is a lot to be said for knowing where that plectrum you want is when you pick up your instrument to play...
I can't really comment on their durability, compared to other brands, being new to felt picks.
Although marketed for ukulele, they work well on nylon strung guitar too.
For the price, I'm pleased.