I forget the exact number, but I lost all of my Rivas (~3) to switch failures and most of my Ego's (Tornados and Joyes circa 8) due to battery failures. Two started smoking and became so hot that I had to toss them into a sand bucket in my garage. Fortunately, I was around to note the failure. This was over a period of about 14 months.
It's the price you pay for having a self contained unit. One supplier (Mad Vapes) reported failure rates of greater than 30% on new units. 6 months ago, I said screw it and swore never to buy another self contained unit.
Things may have gotten better, but the costs just do not justify it. I can get 14500's or other 900 mAh batteries or greater for a fraction of the price of a new Riva/Ego/Tornado. From China with shipping, they average $3 vs. $20. LiIons can only be recharged some 300 times. If you are a heavy vaper (I am), it means that you will definitely fry a battery in less than a year.
Not to mention the fact that dedicated attys/cartos/tanks/accessories are much more expensive than the traditional type. For the last 6 months, I have only been using PV's with non proprietary batteries/systems. I use my two Reo Minis when out and about with LR 510's, several ePowers with tanks and LR cartos, and a BuzzPro and a ProVari with my Vapemates at home. In this time, I have tossed one standard battery. I fried one switch on an ePower, but that was my fault when I accidentally reversed the polarity of the battery in the dark. A new switch was $13.
As typical with these threads, people will say that their units are perfect and that any issues with a unit/customer service are clearly the fault of the OP-in addition to the fact that the OP is a pervert, does not bathe, beats the dog and kids, and spends the entire day in the trailer park home collecting welfare and watching re-runs of Anne Nicole Smith's reality shows and comics.
There have been many issues with everything from PV's to Attys/Tanks/etc. There are some quality suppliers out there who really stand behind the product even when there are design/production issues. Others take the money and run.
Vaping is anything but a plug and play experience. The Ego, despite the issues, did serve the purpose of keeping me off analogs for many months. It does work more or less; there are just many better designs out there, thankfully.