We also use the web version on iPads, but the problem with that is two-fold;
Weekly scheduled system maintenance that precludes using web ESO at all during that time period.
Lost/blocked 3G/4G service can hamper crews from getting signatures.
There are very few Windows tablets/laptops that are as portable as the iPad mini 4's that we use. There are NONE that have the ability to manage, track, secure, and lock down the tablets baked in like Apple does. So that necessitates more expensive and bulkier hardware, plus the additional cost of Mobile Device Management software if you go that route.
Native apps for Android and iOS are such a huge selling point, I don't understand how or why they aren't tripping over themselves to get them out.