I paint pretty much exclusively with the TSC paints.
For the most part I use the TSC primer. For any big jobs i use the quart and gallon can of primer.. for some small jobs I have use dthe bps spray can primer.
In a few situations where i ran out of BPS spray can primer I have run across the street and used (gasp!) wallmart spray can primer for small hanging parts. So far.. I can't tell the difference on which parts were bps spraygunned primed, BPS spray canned primed, or walmart spraycanned primed.
The BPS paint WIL benefit froma hardner.
High humidity and or low temps are to be avoided. I've not had good luck under 60' or much over 90'.. though if painting hot.. you may change your spray mix a tad... I usually use naptha to thin my BPS paint.. but if i had to spray in super hot weather and had no other choice.. i might cut my thinner mix with a hair of mineral spirits so it wouldn't flash off so quick.
I use a respirator with a good organic cartridge, and I paint inthe open air.. ideally with about a 3mph breeze or so.. just enough to keep the vapors moving.
Some people can be very sensitive to the 'iso' compounds in the hardners. While there has been some discussion that the valspar hardner may have less of these compounds than other hardners... it is deffinately still present.
Safest bet is what you've heard.. a forced fresh air breather... that lets you paint in a booth if you wanted to...
If you are like many of us.. you can practice some due diligence and make a good outside spray job with minimal risks.
If you use it.. and even think you might be becoming sensitive to the iso compounds.. dump that spray gun of mix and forget about using hardner unless you get or make the right breather equipment.
By the way.. you can get some pretty superior results with using bps, hardner, and painting outside.