As a Filastruder owner...
There is a reason to shred filament then extrude it, the reason is to get your color mix "perfect". This is why many that own a Filastruder also build small devices that won't chop up random medium sized plastic "things" but do a good job on chopping filament to pellets to re-extrude.
With that said, check out ABS "virgin material" pricing before you decide to start attempting to granulate items into something the Filastruder can use. For most of us that don't own a high end industrial machine, it simply isn't worth the time and effort compared to the cost of just buying pellets.
But no matter what you decide to do, the Filastruder works very well and later versions just keep getting better. The key to using it is to weigh the cost of buying filament over the cost of do it yourself. For instance, while I'm getting a decent return creating ABS filament, it would take a while to get back my investment on the Filastruder and FilaWinder. PLA doesn't seem worth doing at all in my case, but I do VERY well every time I make a roll of HIPS in getting a return on my original investment. Uncommon materials that would normally be expensive filament or "unique" color filament make owning a Filastruder very cost effective if you do that sort of thing.
