With the amount of stims being added together, do you worry about the long terms effects of "preworkouts"?
No, not at all.
Provided you don't have any underlying, pre-existing conditions - the one's I use (ephedrine/caffeine) are safe and effective. See attached study. That goes for both the synthetic forms (ephedrINE and USP caffeine), as well as the herbal (EphedRA, Kola Nut, Guarana etc.) BTW. I have that study too, although its not at my fingertips...
https://www.ncbi.nlm.nih.gov/pubmed/8384186
Unfortunately, the same can't be said about high dose caffeine, plus yohimbe and DMAA, DMHA etc. as far less data is available on those. Yohimbe is downright nasty stuff IMO, and should never be co-ingested with other stimulants. Ironically then, the proven safe/effective E/C combinations are illegal in the US (at least when sold as supplements), whereas the kitchen sink formulas (which are not as well studied/have far worse sides), are legal....