I've never used the hhp-3, but the primary advantage of a purpose-built tool for this is that it should help ensure that the cups are pressed in straight. This can be done with a home-built tool if you're careful during the installation. If you only need this for a "one-off" project, I'd say use the home built version and stay attentive. If you think you'll be doing this on a routine basis (e.g. "bike flipping") get the Park tool.