does it come with mandrels?

yes it does it's color coded ,however this tools is spring loaded not a hydraulic tool which is in my opinion the hydraulic is better but hilmor do not have it.

Can this tool be used to bend 7/8 type L hard drawn tube?

I doubt it, as it's a little rough to use for 7/8 soft drawn. Definitely a great tool for residential Hvac work though

explain the "limited lifetime" warranty

Limited Lifetime warranty does not apply to product that has been damaged as a result of improper maintenance, accident or other misuse, or which fails to operate due to normal wear and tear.