I only have the rear pillion seat and grabrail fitted if I plan to take someone on the back, which really isn't very often, maybe half a dozen times a year at the most. Rest of the time I just have the seat cowl fitted.
We tried those love handle thingies before but the problem with those we found, was that under any sort of moderate to heavy braking, the pillion ends up sliding forward into me, which shifts a fair bit of wait forward and upsets the entire handling of the bike - not good!!!. At least with a grab rail the pillion can brace either forward or backwards depending if the bike is accelerating or braking.
Another thing we found that helped was to buy a roll of that stuff you can see on the rear seat in the pic above. The missus cut a piece to fit and then all that was needed was a long piece of elastic sewn into it underneath and bobs yer uncle - a home made Triboseat. :thumbup