Leaf Spy is more expensive, but much more versital. Much more information and functions LeafStat doesn't have. But if you want the basics, LeafStat is fine, and cheaper. I have both, because LeafStat was available first for iPhone, but I use Spy mostly, I can see my tire pressures easier. Stat uses a smaller font for that.
'12 SL last reading @ 2 yr, 22k, 260 GIDs, 62.35 Ahr
'15 SV w/QC, Mfd 5/14, Leased 8/14, 292 GIDs, 64.38 Ahr when new
@ 36 months, 34k, 270 GID, 57.49 Ahr
'17 Bolt LT
6.72 kW Array