Are they strong enough that you can use the jack as in the weld-ons in your pictures?
I've seen pics of other guys' bolt ons used as hi-lift points with no problems at all and have no reason to doubt these are any less capable but its still always nice to hear from somebody that's knows for a fact rather than my educated guess.
I'm taking a welding class at night at at the county vo-tech to remedy this welding dilemma (for $160 I'm all over it) but I have to wait till the fall semester. If the bolt on will do the job there's no need to wait. 90% of my reasoning for wanting sliders is for a hi-lift, I don't do any crawling.