Long reply based on my uni days - read if you can be bothered.........(mods feel free to delete if this is not welcome - bear in mind it's facts, not an endorsment)
On a purely scientific basis they should work as a high proportion of 'new breed' pills comprise of chemical substances that have a proven stimulant / hallucinogenic properties.
BZP based 'pep pills' are actually extremely closely related chemically to phenethylamines such are the much loved 3,4-Methylenedioxy-N-methylamphetamine and as such I can't see them remaining legal for long. (If it's your thing, enjoy them while you can I guess)
A word of warning though, while currently legal, do not take this as a guarantee of being without risk - benzyls such as this have been through (very) limited human testing - the fact there is little chance of them being used as a profitable medicine, means research by the majors has been limited.
As they have very similar stimulant / hallucinogenic properties as a number of currently prohibited drugs (and a similar effect on the body) it is scientifically reasonable to expect that many of the potential health risks associated with will also be shared. Common side effects (would be expected to be) qualitatively similar to those produced by amphetamines and methamphetamines such as increased pulse and heart rate and nausea. Higher doses (overdose) could cause restlessness and anxiety, adrenal disorders, dizziness, insomnia, tremor, rapid pulse, sweating, respiratory difficulties, confusion, hallucinations, delirium, and (very infrequently) convulsions. The most dangerous side effects of overdose could be stroke, heart attack, abnormally high blood pressure and rapid, irregular heartbeat.