I put one on my 208 after a couple of years and was one of the first things I did when I bought my 258. I think its a good idea for several reasons:
1. If you are likely to beach your boat, intentionally or not, it will save any abrasion on the keel.
2. If you sometimes bump a cross member while loading or unloading your rig at the ramp, ouch!
3. The unseen stray (small) floating object.
One tip: I had every intention of tailering my 258, which I did for the first year, so I bought the almond colored Keel Guard which matched the gelcoat perfectly. Then I decided to slip my boat and painted the bottom black around the almond Keel Guard. Not so pretty :cry:. You want the Keel Guard several inches above the waterline. I know I'm being picky here but I couldn't live with that so I stripped the almond one off. WOW, what a job that was!!!! I replaced it with a Black one and that was that.
I think it's worthwhile for a little piece of mind.