Polyester Capacitors for pulse applications
Dielectric absorption (DA) is much (5-10x) higher for polyester capacitors as compared to polypropylene, so losses will be higher, which could cause problems.

There may be other differences in construction that would affect pulse applications, however they are not inherent to the choice of dielectric. 

Edit: I don't think the capacitors you show are necessarily suitable- the pulse current could be very high, which those parts are not designed for (my second original paragraph above). Consequence could be slow or rapid destruction of the capacitors as the metallization blows off the mylar and perhaps shorting of the plates. 

There are other types of capacitor easily available which could be substituted but I think I'll let others suggest them. This seems like a pretty dangerous project.