I have a Provari, several ego c-twists, and the itaste. They all are great for specific reasons.
Ego-C Twist: Great device. Use everyday for commuting. Easy to carry, lightweight in the purse and in the hand. Works well. I carry two to ensure I have enough battery for the day.
ProVari: Great device. Use everyday - sometimes when I am driving - but always at home. It just works rock solid. My only wish is that it were a little bit lighter. Gets heavy to my little girly hands sometimes.
itaste: My least favorite is the itaste - for the very reason I thought it would be good - the square shape. It just looks funky with round tank types. Cartos look fine. It does vape well. And if you lay it down it doesn't roll

. lol.
In summary - I can highly recommend the Ego-C Twist as a great VV device. They are a stroke of genius. ProVari is also highly recommended. But get what you can afford now. If you get an Ego C-Twist or two, and later get a ProVari, you will still find your Twists handy. It is not money wasted.