It's not just Idev's checkout though but unfortunately so many other OnePageCheckout solutions as well.
The thing here is to effectively arrive at a solution and track errors. If you purchased the module, get support! If not, I suggest you install better client-side (mostly Javascript) error tracking such as TrackJS. http://trackjs.com/
Server side, just rely on exception logs and web server logs. Better yet, get NewRelic, too.
There's no shame in using tools. Finding out which works tends to be a battle in itself.