My first iOS device was an early iPod touch and I seem to remember downloading 'brushes' and failing to do anything of any precision on it due to the limitations of the device, the earlier iteration of iOS and my big fat fingers. I haven't bothered even trying to draw anything on a phone sized device since. So today I thought I'd try the mobile version of sketchbook,(and blog the results in the phone blogger app) it works predictably within the limitations of the tiny screen.
It has 3 layers, which is nice, and the same puck to control brush size and opacity as it's iPad cousin.
The only slight fiddle is the need to relaunch the pick menu after each selection, so pick a brush, open it again to pick a colour or change size.
That said there is a really useful quick colour pick tool, a long press opens a crosshair and means you can switch back and forth quite nimbly.
As with all touch devices sometimes the gesture recognition fails and instead of the crosshair you draw a line, and then have to open the picker to undo.
It would be worth trying this app with a stylus to get a bit of precision in the lines, but I think you'd have to be quite dedicated to not just use a real notepad and pen... Which of course you could photograph and bring into the app as a layer to be worked up into something fancier.
The other big downside is that using the app does seem to hammer the battery of he phone, so it wouldn't do for a long day of sketching... I guess it might work better on one of the fatter bigger iPhone 6s?
So why would you use a drawing app on your phone?
How about if you were on the train to Yorkshire to see your dear old mum? (You'd use your iPad if you had any sense)