When I got my TR I was all gung ho on getting an extended battery and would likely have sprung for an outboard charger, were one available. For a number of reasons, ranging from price to shelf life, I decided to hold off and see how the standard battery met my needs.
Unless someone is really ripping through battery packs I don’t see much value in an outboard charger. If push comes to shove, I can usually find an outlet or top the battery off in my car.