First and foremost one has to really, really, really, really want to stop smoking. If there is an inclination to still enjoy a cigarette, the cigarette will likely win.
Next is a trial and error thing with vape devices if they choose to substitute one for the other. Usually if it's complicated like batteries needing charge in a special charger, has a 'fire' button and/or other things to get used to that may cause them to decide on ease of use and click the BiC again.
Let's face it, the Juul or other cig-a-like devices make great starters while getting used to being tobacco free. Portable is also another key to successful switching. If it's as big as a tv remote control most newbs won't dig that for long.
It's natural to think tobacco flavor is a good starter flavor. Trouble is most don't taste like that Pall Mall or Newport. Fresh picked 'backee' drowned in maple syrup is more likely. NET (natural extracted tobbacco) is typically a pretty good mimic, but can be costly versus the fake stuff since it takes a while to brew small batches properly.
Some dig on food flavors and deserts. I go for chewing gum flavors like fruit gum or dentine mint. I found a vanilla ice cream-ish flavor for vaping with coffee.
Devices to start should be easy to use, provide a good "drag" and have enough nicotine content to satisfy without chain vaping, which can 'hot box' the coil pack and lead to premature "yuck-o" flavoring. Simple is best. Draw activated is popular for a good reason, yet many like the fire button type better to give a stronger vape with each drag.
Check out the pod section for a bunch of choices. Small pens used to be wildly popular for good reason and many vape-vets still use them.
Most important if dual using is DO NOT smoke then vape or vice versa. Do one or the other. Say you smoke with morning coffee and vape 'til sundown. Each day smoking less and vaping more over time. I made the mistake of vaping and smoking throughout the day and now my brain thinks a drag of vape signals a drag of cigarette soon after.
Best of luck with your friend.