Previously, I used a questionable copy of MyWi4 since the developer charges too much for the app. All I got is a unstable iPhone when I tether it to my iPad. The reason being is that the web browsing experience is better because of the bigger screen and the 3G version of it was not worth it.
I decided today I had enough with miwi, so I took the native tethering route by installing a carrier profile that enables tethering and bought iTether on the iPad, which costs $5 (15 dollars cheaper than MyWi). So far, there is no difference in speed and the iPhone battery doesn’t drain fast after three hours of use since it uses Bluetooth PAN.