The major advantage to having liability on your atv policy is that your umbrella insurance is excess insurance and cover above and beyond after your other policies pay out for claims. Also umbrella underwriters tend to cancel umbrella policies after so many claims (usually one or 2 within a 3 year period depending on the size of claim) The more liability insurance you have specific to each policy usually means the better you are protected for occurrences pertaining to that specific exposure. While an Umbrella may provide you with the protection you need for liability in certain instances it may not. For instance my boat insurance with GEICO is a stated value policy with a value of $20,000, and provides me with 100,000 combined single limit bodily injury liability and 50,000 property damage liability for $220 per year The protection is specific to the liabilities involved in boating and water sports as well as the property associated with the nature of the exposure as well, also it includes perils like oil spills and covers up to 850,000 in liability for oil spill clean up and boat recovery in the instance of my boat capsizing or sinking. My atv insurance costs me about the same for 100/300 and 25,000 with a $100 deductible for comprehensive. My atv policy has my mods listed and would be considered in the adjustment should anything happen to my quad. However, I never asked for an agreed value policy, which we may offer.