No need to carry paper
I have used SkyCharts exclusively for the last several months in all conditions. Heat has not been a problem - although I have mine laying on my lap or on the seat next to me and most of the time I have the case closed. I use it pretty much the same as I would a paper chart - handy, but not necessarily open for the whole flight. It has been great for the flights that change over from VFR to IFR too, just touch the button in the upper left corner and switch to the Low Altitude Enroute chart and you continue to have your course line to follow along with the airplane icon tracking you. Want an approach plate? Tap on the airport you are interested and there is a list of all approach plates and the AFD for the airport. you never have to worry about having everything you need, unless of course you didn't download the area you are flying in. SkyCharts now has the US broken into segments, download the SE US and you will get all charts and approach plates for the SE, and the program will let you know what the cycle is for updates. Updates are downloaded anytime you are on Wifi.
I haven't experienced any problems with the GPS finding me, even when I haven't started the app until airborne, it has found me within a few minutes and has never lost signal. I don't have the external attachment for it. I could see where someone in a Spam Can with no visibility to the sky may need to put an external antenna up on their panel, but I wouldn't invest in it until you try the internal gps. Even the accuracy has been great. With three other GPS' in the plane, I don't necessarily need the ipad GPS, but it is great to have it tracking your position on the chart.
I started with SkyCharts by recommendation from a friend and reviews on here. You have to take a look at what your mission is. I didn't feel like I needed all of the bells and whistles that ForeFlight adds, and their "Free Trial" doesn't do you much good to tell how it really works since you are very limited in what you can do with that version. Once I got going with SkyChart I never looked back since I was very pleased with what it offers.
Maybe my expectations for an EFB are low, but what would make it worthy of being primary for charts instead of supplementary? It hasn't failed me once in about 40 hours of cross country flights. If it does - I have the 430, 496 and Blue Mountain that can all get me where I need. Honestly, 95% of my flights I don't find a need to pull out any chart - paper or plastic