I did... And I wouldn't look back...
The lack of mobile apps is easily offset by the availability of full fledged Windows application. Dollar for dollar and pound for pound it's a no-brainier.
yeah, i actually don't use a ton of mobile apps. Instagram, Facebook messenger, snap chat about sums it up. My main focus would be reading/highlighting PDF and EPUB, note taking, forum browsing, and media playback.
As an Ipad replacement? Idk about the Surface 3 but the Pro 3 is much to large and heavy to be used as an ipad replacement it's just not something I would recommend trying to hold for any extended period of time with one hand.
The Surface 3 is .4 pounds lighter but I can't see that being a huge difference when the ipad .3 lbs lighter than even that (.76 lbs lighter than the pro 3). You can certainly try though. Let me know how it goes if it is light enough I might get one.
Added
I played around with the Surface 3 and Surface Pro 4 today for about an hour at Best Buy and I can say with confidence, Surface 3 is a joy to hold at a little over 10 inches, definitely the best iPad replacement out of the bunch in form factor, it's really perfect IMO. However, despite the 12 in. screen of the Pro 4, it really isn't that heavy to hold with one hand, in fact, it's very light, and the only reason I wouldn't consider it is mostly for form factor and what can easily fit in my book bag etc...I was using the i5 model and it was blazing fast, really, fell in love with it and the pen in just a short time with it. Still, I don't think I would really use the power, I just want a personal PC for web browsing, note taking, and PDF/EPUB files. I think the Surface 3 would suit me, but being a gamer, I do like to have the extra power.
Worth
Also if you don't get any of those, the iPad Air 2 is a great iPad and super fast - and the 2GB ram makes a big difference for things like safari.
yeah, Air 2 has a bit better screen than Surface 3, but tbh, I'm really a huge fan of the pen after using it. For me note taking, highlighting PDF files are # 1, and Surface is superior in this regard. Sucks though, I do like apps like Snap Chat and Instagram, and this is where Windows store is still lacking, mobile apps.