So I tried iQOS at the weekend. It's very similar to vaping loose leaf, though more user friendly as it has disposable 'heat sticks' which can easily be swapped out. Disposability is great for convenience, not so great for the environment, though I'm told the plastic in the heat sticks is food based and biodegradable (not sure about the filter tip they use). The heat sticks contain very little tobacco but it is apparently concentrated in some way. The tobacco is packed in straight tiny strips cut from reconstituted sheets.
In terms of direct comparison:
Vapour
Same kind of vapour (i.e. tobacco + VG) but the amount it produces is regulated in the iQOS so it is more consistent. It is possible when vaping loose leaf to take a hit that is overwhelming whereas the iQOS gives more consistent hits. This becomes less of an issue when you have experience of vaping loose leaf as you just get used to how to use it - giving you freedom to use as you wish. Once you are used to vaping loose leaf, it is possible to replicate the iQOS experience almost exactly. Bite and satisfaction of iQOS is basically the same as vaping loose leaf, which makes sense as it's the same concept but the iQOS uses a heated blade that conducts heat through the tobacco whereas my vape uses convection heating - known to be more effective than conduction approach and less likely to accidentally combust. Loose leaf vaping is done at a much lower temp.
Flavour
This is obviously subjective but the flavour from the iQOS is similar to loose leaf but not as nice - has a distinctive twang which I didn't like. The tobacco in their sheets has been treated (with VG among other things) and I suspect there may be some flavouring added (maybe to try and replicate the Marlboro taste). The loose leaf vape easily wins on this front, with a lovely natural, clean tobacco taste. The residual vapour smell from iQOS is similar to loose leaf vape (both disappate quickly).
Convenience and cost
iQOS is more convenient but the cost of heat sticks will add up quickly when compared to loose leaf. In the EU, we may see the price of loose leaf go up significantly over the coming years so this cost difference may become less significant. Much more waste with the iQOS. The way I like to compare is to say loose leaf is like smoking a pipe, iQOS is more like a cigarette. Probably two distinct groups of users. One heat stick didn't seem to last as long as one bowl in the vape. iQOS has a slicker design than all the loose leaf vapes with a very compact mobile charging unit. With the loose leaf vape, I'm having to use liquid VG whereas the iQOS uses treated tobacco. Carrying the VG and adding a drop every time is inconvenient, but more like loading a pipe than using cigs.
Battery life
This is the only area where for me the iQOS shines completely over the loose leaf. The cig bit slots into a charger device when you've used it so gets charged in your pocket/bag before the next use. You get 12 puffs or 6 mins of vaping per mini-charge and the charging unit itself needs to be charged each day. The Crafty loose leaf vape provides 4 (sometimes 5) smokes per charge and takes another 1 & 1/2 hours to recharge. At +20% charge you can use the crafty while plugged in. Crafty uses micro USB charging. Its older sibling, the Mighty, will provide 8-10 smokes per charge and can be used with a flat battery when plugged in. Has a non-USB charger.
Personally, I prefer the loose leaf vape. More freedom around tobacco (could even use flavoured tobacco) and provides a cleaner flavour. Charging is an issue but I carry charging packs with me. If the WTA does not work out for me (still waiting for it to arrive), I may well invest in an iQOS when it becomes available here for those days when I need to be out for a whole day with no room for extra chargers etc. The cost of heat sticks would become prohibitive to long term users of cheaper rolling tobacco though and the waste element will frustrate eco-aware users. It does have the convenience element going for it so there's definitely a market I'd say.
But I'll stick to loose leaf tobacco. And if you want to avoid the Big Tobacco companies, it's the only way out of the two.