I've used their engine flush. It's not the same as the flush you buy elsewhere. You pour in the flush and
drive your car around for another 10-20km and it sort of changes the dirty oil into some viscous mix. When you drain it comes out watery and white, then anything caught in the flush comes out quite interesting small chunks. I use another bottle of cheap oil to flush again after that and the oil comes out the same colour it goes in. Not much left inside the engine.
Oh this is my writeup :
Product testing : Blue Chem fuel system clean
Incidentally - why do you use so many flushes and cleaners? If there's no need to do it then you don't need to do it and there's no benefit to do it. Your cash your choice though.
1. Last time I paid RM240 for 4 injectors. But that was a while back - I don't know how much it is today. Try asking shops for a quote.
2. Usually it's a as and when situation. Cuz if you have access to poor quality petrol then it'll potentially be earlier. Just monitor your fuel consumption and power. If there's a drop and you've checked and replaced other things then it's probably a good idea to clean.
3. Usually if you are there at the shop you can see the actual cleaning itself. When I did it at GTAuto the boss did it while explaining how the cleaner works and all and showed me everything. Depends on the shop I guess.