Like I have already posted on FB. Maybe some of my personal experience can be at help here.
first i will say EFI live= Hptuners they are both great softwares and can achieve the same things in Gasoline tuning its mainly personal preference.
I chose HP tuners because of the simplicity and user interface. Once you become familiar with the relationships/values/interface it'll begin to make sense to you. I know for me that was the largest issue was actually knowing what the values of the numbers represented. I'm no professional but i do know the basics, I'm self taught with the help of the hptuners forum and by a local tuner who only tunes for himself who happens to be a friend of mine. EFI live i seen and clicked around with, i really did not like it all it seemed to be for more of a professional, was very in depth and I disliked the user interface design and the way it was organized.
Hptuners has small dialogs that pop up when you hover over different charts briefly explaining what the values are and exact what they do/change/affect. The interface organizes all of the tables very nicely in a sort of manner that allows you to find and adjust what you want even if its your first time ever opening the program. The forum and support for HPtuners is great. By explaining your troubles and uploading the tune file and log file, the guys there most of the time can help guide you in the right direction to correct the tuning issue you are having and explain further on. Learning the software does not happen in hours/days/weeks but months. I spent countless hours of adjusting and data logging to see what exactly I was changing and doing and how it affecting the truck. There are plenty of write ups and tutorials to follow to aid in tuning for a cam/nitrous/boost... just about anything. The tune depository is also a great tool, it stores tunes that everyone uploads for others to use, by simply applying your model vehicle it will populate a list of different tunes for X mods. Your able to download and use tables from those tunes if your unsure/missing/needing/referencing.
When/if you purchase hp tuners it comes with hp tuners vcm suite and scanner. The scanner is a powerful tool to use not only for tuning but its amazing for trouble shooting if you know how to use it. There are over a hundred sensors and pids you can pull up and view in real time. It very important to learn how to use/read/setup this scanner to view what you need and properly calibrate and change what you need in a tune. Tuning and punching in numbers to fill data columns and rows is one thing, but its no good unless you can data log save and review to make sure the data entered is safe and isnt hurting or hindering the performance of the vehicle.
One thing I wish i had and will eventually do, is get a wideband o2 to use with hptuners. It makes things alot simpler. Another thing to note, Im unsure now but when i bought mine it came with 8 free credits, thus enabling me to tune 4 gm trucks. credits are 50 bucks a piece. some vehicles require more than 2 credits, but once you run out you will start having to buy them to edit and flash tunes to vehicles if you ever begin tuning for others.
As said above, which i too have done. You can email your tunes and logs to other tuners with Hptuners for them to assist you if they are willing. Just like using the forum. Some may want a few bucks but its better than driving hours away.
As you said above, little to no down time. its possible hell it took me 20 minutes to get my truck to idle good and run decent and drivable. However to get a 100% tune and WOT and perfect it may take you awhile to perfect. It goes back to understanding how to data log and what to adjust get a desired affect
Sorry for the 100000 grammatical issues. If you have any questions post, and ill try to answer them as best as possible