An SEM user will never get an image that is better that the scintillator! So while one might cut back on the quality of other aspects of their SEM's system's operation, the quality of the scintillator is paramount in terms of getting the best possible image from your SEM.
Basically it is the classic battle of the trade offs! The SPI P-47 powder scintillator is the one with the fastest response time, which is well under 80 ns. However, the system itself, which consists of the powder scintillator material dispersed on a high optical quality substrate designed specifically for this application, and a proprietary polymer acts as the "glue" that binds the scintillator layer to the special substrate. In the earlier days of SEM, scintillators tended to fail by peeling off, but today's technology permits one to make scintillators where this mode of failure just does not happen anymore. SPI guarantees its scintillators against failure by peeling or delaminating.
The single crystal scintillators of YAG and YAP in comparison indeed do last forever and will outlive the lifetimes of most scanning electron microscopes. However, the single crystal scintillators of YAG and YAP exhibit slightly slower response times than P-47. Note that in the graph the caption "2 mg/cm" means 2 mg of scintillator powder per square cm of scintillator area. The biggest improvement of a YAG or YAP over powder scintillators will be for those with relatively clean vacuum systems. If the vacuum system is an especially dirty one, one would have to conduct a periodic cleaning in order to maintain the favorable characteristics of the single crystal scintillator material.