There is no such thing as a drug (herbal or manmade) that doesn't have a side effect, so when the ads make this claim, I'd start getting worried about what else they are lying about. (Even water has a side effect....it makes you urinate more).
active ingredients (ingredients taken from one of the VigaPlus websites and the herbal drug information comes from webmd.com):
Tribulis Terrestris - drug interactions with beta blockers, digoxin, an calcium channel blockers (so don't take if you have hypertension or cardiac issues); it can mess with your blood glucose levels (so don't take if you have diabetes); and has been linked to prostate problems (which can be the CAUSE of ED)
Withania Somnifera: don't take if you have a stomach ulcer, it can serve as a trigger for autoimmune diseases such as MS, rheumatoid arthritis, lupus, or other like diseases, and don't take near a time of surgery because it may effect how the anesthesia works.
Chlorophytum Arundinaceum: not enough is known on how this drug acts
Mucuna Pruriens (and L-dopa or levadopa): may change blood glucose levels (use with care with diabetes); use with caution in people with cardiovascular disease (low blood pressure, fainting, dizziness, and irregular heartbeats); can make liver disease worse; and can make mental illness worse.
Myristica Fragrans: dangerous in doses greater than found in food (hallucinations, seizures, death... (not sure what the dosage in VigaPlus is)
Piper Nigrum: only suspected to be dangerous in very high doses (but all it is a type of black pepper)
It may be "safe" if you have no health problems....but if you have ED, you have at least ONE health problem. Go find out what is causing the ED before you start playing around with untested, unregulated drugs...and that is exactly what most herbal supplements/drugs are.