I have/am using both. The eCab sits between a 510 and an eGo C. It does has its place in a vaping arsenal and performs really well. There are 2 downsides to the eCab. The 10440 battery and the proprietary threads. Now, to many this may seem a let down from Joyetech but forums represent only 10% of the vaping population and there are a slew of individuals that do not like big honking mods. Proof in the pudding folks would be very surprise to find out the amount of eGo vapers that were tooting on an eGo at Vapestock. Yes there were mods galore ect... but the eGo had a stronger presence than I anticipated, considering it was a vaping convention.
The 10440 battery cannot support LR vaping and hence why it lost popularity over the up-coming 18650 in the day. Then again that was comparing apples and oranges. If one is looking for a discreet classy PV that can support 3.5-4 hrs between charges, then yes it is a good device, especially with the ladies with an evening purse

or even men at a fancy venue.
IMHO folks need not compare what works for them to suit their vaping style and quash a device "in general" because it doesn't fit their lifestyle or vaping style. OP asked for an opinion from someone who has vaped both. For what its worth I get slightly less battery time out of the eCab when comparing with the eGo Twist, but then again it is dependent on voltage (4-4.5 hrs on the twist). BTW it is a great device to take to the movies or dinner