I've only tried taking this stuff orally (bombed in a rizzla, disgusting taste), and it worked like a charm. As knocando mentioned, 50mg is probably a good starting dose for an opiate naive user. If it's a little weak, top it up in 10-20mg increments until you reach where you want to be. Max dosage I took of this stuff was 100mg over 4 hours, and it had me in a very pleasent place.
Most of all, keep safe and don't cane this stuff too much. Have a feeling it could be very addictive, and pretty easy to overdose on if you get too carried away.
Don't mean to scare anyone, but with this chemical having such a similar structure and range of effects to tramadol it might have the potential to induce seizures at moderate to high doses; probably best to stay away if you have a history.