There are many things wrong here. First of all how did they obtain the footage? Why would ISIS reveal identity of it's techie's? And how are there no workplace accidents which should be a common thing considering they are working with 'homemade' approach? Edit: Now see how they got footage.
My initial thoughts, their car bombs usually are primitive and filled with boxes/gallons of explosives. I don't see anything new here besides trying to man a car. Which I don't believe they achieved or how they achieved it. The 'converting bomb payload to anti air craft' part was hilarious and not possible. Don't know where these journalists got 99% success figure from.
Anyway I don't believe this is showing us anything new besides some primitive experimenting which probably ends up getting them killed. Even professionals working in home environment doing these things with their hands will run into many accidents. I say this because in Palestine everything is hand made. The rockets, IED, rocket propelled grenades, etc....and there have many incidents where something explodes prematurely.
The latest operational tool I've seen being used by ISIS is Katyusha rockets which are easy to produce and made by all militant groups. The group is still primitive but has lots of experience. The bigger issue is the lawlessness in Iraq/Syria making it easier to procure materials. You can get away with anything even in the capital of Iraq. There is no organized security force or useful intelligence so they will have trouble prevent these bombings.
