Both up tolerance as far as the sedation effect is concerned, so if you are using them for this effect, then its probably best to use them short term only. I've never noticed either to be 'as addictive as GHB', certainly no more addictive than diazepam, ime. If taken continuously, without upping the dose, the nootropic effect of increasing mental capabilities is uneffected, and I find that the tolerance does not build beyond its initial point, as long as you don't give in to the addictive urge to up the dose for more sedation. Thus, a larger dose can still be used to relieve insomnia while you are taking them, as long as its done for only short periods.
Picamilon is GABA attached to a niacin atom, allowing it to cross over the BBB, where it has both the sedative effects of GABA, as well as the stimulatory effects of niacin. I still don't know if the ordinary GABA supplements with niacin could actually work, though. If so, then picamilon could actually be an endogenous neurochemical.