In my experience, boosting filament delivered the shortest amount of service life of any method.
Back in 1981, RCA had a short run of bad HV transformers (quickly resolved). The trans was mostly conventional but had a single brown wire for CRT filament from one of the exterior terminals that went to the CRT board. As originally installed, the wire was routed between the metal frame of the trans and the chassis (metal back then).
If the trans was replaced and the brown wire was routed by the core and not between the frame and the chassis, the filament would pick up a few hundred milivolts by induction and add it to the normal 6.3. Several months after the trans was installed, the CRT would be shot. Fortunately, this happened in warranty. RCA quickly added a bulletin and a service note in the replacement trans that described how to properly route the filament wire.
Zenith in the 90s had a bunch of tubes suffer heater to cathode shorts. Most guys would thread two or three turns of bell wire around the HV trans core and feed the filaments directly (after cutting the grounded filament circuit). This would allow a full floating filament supply that wouldn't pull the cathode low even if the fil should short to the cathode. Problem was, guys would just wire so the filament looked the right color temperature but if the final voltage was much above 6.3, the tube would tire in a few months.
The solution was to use a TRMs meter (15K cycle AC from the fly) and adjust with winding count and/or a resistor to ensure the filament stayed at or even a bit smidge below 6.3TRMS AC. I did those and got many years out of those repairs.
Going back farther, we used to install hang on filament boosters in TVs with weak tubes to allow customers time to either save for a new TV or a CRT swap. Typical life of a boosted tube was two to six months.
I bought a new B&K 467 (still have it and two others from closed shops) and the life of the CRTs after boosting was 6 months to two years. The Sencore was supposed to be better but I never had one of those. In any case, we never sold a boosted tube of any type.