Sometimes you do better with painter's tape at 1/4 inch. I've had that guide jump over fabric and wind up on top. I have one for the Pfaff and usually grab the foot without the guide. I don't care for the clear guide, but do like the metal one. All of Pfaff's use the IDT.
Learn to use the markings on the foot. That will save you more hassle than the guide.
The regular foot on the 1500S is not a full 1/4 inch. I use it for scant. But no markings. A sharpie and the regular quilting foot as a guide fixed that.