I've never used one; not hard to understand how and why it works, but I don't think it's appropriate here. When you look into them, you find assumptions like "pickup truck" and "trailer weight 5000 lb and over", so that suggests that they're pretty severe overkill for this application.
I just got back from the scales, and the weight came in at exactly 700kg (1540 lb), which isn't a surprise given the published weights don't include the added front wheel/stand, boat mounts, gear stowed in the sailboat, or (probably) the gas in the jet ski. So the question now is what the actual tongue weight is and whether it can be dialed in to ~150 lb, which is pretty modest. And since it's a 20+ year old car it seems to me that the springs are softer than they should be, so does it make sense to add all that heavy-duty hardware to correct what's really a pretty small deficiency?