I did Bimix injections for almost 18 months, and never once had bruising.
I always took care to get all the air out of the syringe -- held the syringe with needle up and flicked with a finger a few times to dislodge any air bubbles to the top. Then squeezed gently on the plunger until all visible air bubble was gone and one drop of fluid appeared at the tip. Then drew back slightly to draw the drop back into the syringe -- didn't want to waste any.
I later read in this forum that injecting a little air did no harm, so now think these precautions were over the top. If you can contrive to have only air left in the syringe after injection that should lead to minimum wastage. I figured with my no-air technique, there was about 0.07ml of fluid wasted. If I started with 0.07ml of air in the syringe, then a slightly downwards injection angle should leave mostly air in the syringe with very little wastage.
Of course it is hard to estimate 0.07ml of air, so in practice I would have settled on 0.1ml of air, and maybe injecting just a small amount at the end -- but not enough to cause bruising or other side-effects.
No symptoms; PSA 5.7; Gleason 4+5=9; cancer in 4/12 cores
Non-nerve-sparing RRP 7 March 2008 age 63
Organ confined, neg margins. Gleason downgrade 4+4=8
Bimix worked well; now using just VED
PSA undetectable at first but now 0.4, doubling time 7 months
No radiation but ADT coming unless I can slow down the rise...