Photoroom starts from your photograph and makes it usable. Backgrounds out, framing standardised, output sized for a marketplace. Its whole design points at doing that a thousand times so a catalogue looks like it came from one shoot.
Pebblely starts from your photograph and puts something around it. A surface, a setting, props, light. That is a creative act rather than a corrective one, and it produces images that are more interesting and less predictable.
Consistency is where they separate, and it is not a feature either can bolt on. Generation varies between runs by design, which is exactly what makes Pebblely feel useful on the first image and awkward on the fifth. Correction does not vary in the same way, which is what makes Photoroom dull on the first image and reliable across a listing. Neither helps at all if the product has never existed physically, which catches a lot of print on demand sellers who arrive here by mistake.