The Only Draw Back I,ve Found Is Recoating it For Touch ups without the Hardner in it . Still Need a Good Charcoal Respirator
As he is alluding to, acrylic enamel without hardener will want to wrinkle like you put stripper on it, if you ever try to repair it, or if you mess it up and want to reshoot it.
The safety equipment for this product with, or with out hardener, is exactly the same. If your going to worry about the iso that much, you need to realize the paint, and reducer still have dangerous chemicals. It's like a bear that still has three sets of claws.
In a case like acrylic enamel where using hardener is optional, the name hardener is not really correct. The hardener is a resin that changes the chemical make up of the paint, and converts it to a higher quality finish by increasing adhesion, as well as gloss. The end result is a paint that is no longer soluble, meaning it can't be softened back into a liquid with thinner, as it can be if you don't add the hardener.
A low end urethane is usually only going to be a few bucks more, and not only dry much faster, but be a much better quality. However, with a urethane, you must add the proper amount of hardener, or the chemical reaction that sets it will not take place, and it will not dry.