While LawDog's points are well taken, the bullwhip is a niche weapon that can be very effective in trained hands. It is just not one with a popular real world following right now and unfortunately has a very romantic cinematic image. In the Filipino Martial Arts (FMA) I study there is an old tradition of using either a bullwhip in the 6 to 8 foot range or a short flexible reed type whip approximately 3 feet in length with a close range bladed weapon in the other hand. Not many instructors teach the whip as it is not emphasized as strongly as the other weapons (e.g., knives, swords, sticks, etc.) in the FMAs. Of the several FMA instructors I have asked about whip training, many had trained with it, several suggested that space in their dojo was too limited to train with it, and almost all of them expressed a desire to learn more about their use as a weapon.
Whenever the discussion of the bullwhip comes up, the mention of a determined aggressor charging past the snapping whip is brought up and emphasized. While this is a realistic possibility, I firmly believe it is the exception and not the norm. I submit to you that the majority of bad guys out there are cowards and blowhards that will turn tail the moment their illegal activities become somewhat difficult. To describe the wounds inflicted by an 8 foot bullwhip as making a BG's job more difficult is an understatement.
To me, the bullwhip is also an extremely versatile tool. Beyond it's use as a weapon, It can serve as a expedient 8 foot of lifeline to throw someone you're trying to pull from the water out of a hole, etc. Small to medium sized animals you do not wish to kill can be humanely repelled with it. In a defensive role it can be used as an impact weapon coiled if the handle is weighted properly (e.g., shot loaded) or used as a garrotte if necessary. It also allows you to keep BGs at a greater distance than pepper spray. Of course, one could always use it for its traditional purpose of spurring on cattle and horses if one is so inclined.
The bullwhip also has the virtue of not being banned from carry in Texas. Unfortunately, with or without a handgun carry permit, Texans are forbade from carrying "illegal clubs" (expandable baton) and "illegal knives" in public. maximum legal blade length is 5 1/2 inches single sided. As for carrying it concealed all one must to is mount it coiled on the offside of a shoulder rig under a light jacket. A shorter 6 to 8 foot whip coiled can be quite easily concealed with a little effort.
So when it comes to less than lethal force in civilian hands in Texas, you have a choice of a Taser gun, pepper spray, or a bulllwhip. Each has it advantages and limitations. Personally, I don't trust the Taser quite yet, carry pepper spray daily, and recognize the aerosol's many limitations. I'm planning on adding a whip to my kit in the future once I feel competent with it. In the hierarchy of force the bullwhip falls between pepper spray and a baton, or perhaps even with the baton.
The final decision is a personal choice. Make it realistically and choose wisely.