Vallejo has 4 lines of model paint.
Model Color, approx. 212 colors, more designed for brush painting, can be thinned easy enough (especially with their new thinner), and yes, some colors do have some heavy metals like Cadmium in them, but they are in such small quantities that you would have to swim in a vat of it for a month, and ingest a fair amount for it to be of any harm. Probably more harm done to you being out in the sun for 30mins, however because they do contain these items, they have to put on the bottles the warnings of "Do not spray".
Panzer Aces, 48 colors, same consistency as the Model Color, specialized line for uniform colors, and some special effect colors (rust, wood, rubber, etc,)
Model Air, currently 110 colors, going to be expanded to 125 or so in the new year, pre-thinned for airbrushing, alot of matched RAL, FS, and RLM colors.
Game Color, 90 or so colors, more for the War Gaming market, but they do have some interesting metallic and flesh colors that are only available in that line. Supposed to have an additive to them to make them a little more durable as the figures are handled during the games.
As well you have a line of 16 colored primers, basically paint and primer in one.
I wouldn't really call Vallejo paints "fragile" no more or less fragile than any other acrylic paint. Most acrylics don't possess the catalyst in them to help them "bite" into bare plastic like an enamel or lacquer paint does, which is why they usually require a primer on the kit so the paint has something to bite into.
Once cured, Vallejo paint is one of the toughest out there.
However (and this is borrowing a line from Ken), what makes Vallejo so good at being tough....makes them not so good when used as a color coat over hairspray or the AK Worn Effects, or Heavy Chipping fluids. They are hard to come off, and usually come off in sheets and chunks rather than the more controlled chips.
Tamiya thinned with water instead of alcohol or their own brand thinner is about the best out there for using over a chipping fluid.
That being said, I use Vallejo for about 98% of what I do, and select few other brands for those other jobs that Vallejo isn't as good at.