Quickly/effectively erasing tape reels

Hi!

Currently I've come across a beautiful Teac - 3400s reel to reel. I have been buying used reels with pre-recorded material on them with the intention of erasing it for my own use. My method for this has just been to record over the existing material as I go. The problem with this is that i've been getting artifacts that haven't been erased from the previous material.

Would I be able to use one of these to more effectively erase the tape?

Tape Head Demagnetizer

or this?

I'm not looking to spend a ton of money. Any info/help would be appreciated.