Well I have to say I am sold on the wet palette for my vallejo paints and I have even experimented with paint from the flip tops as well and things have flowed much better.
I will say one thing though you do need to experiment a little with the amount of water inside your chosen container, to make everything work as it should. Its not hard to get the levels right but I do think its a matter of personal preference.
I have certainly saved a small fortune on my DIY version compared to those from art stores. During my Google searches there were three main components for making one of these and they are as follows.
1. A shallow container with a suitable lid
2. sponges or paper towel
3. Baking parchment or greaseproof paper
That is all that is needed I went out and bought the requisite items and spent under £2.00 on the lot.
The container was a total of 60p, the packet of sponges was 50p and the greaseproof I liberated for nothing from the wife's cupboard.