At least in my 452s and 453 (I haven't tried a 455 yet):
Old world craftsmanship and quality that most other manufacturers have either abandoned or charge a fortune for.
Accuracy with sporter-profiled barrels that only a handful of much more expensive guns can exceed.
Better reliability and durability than almost all others, including the more expensive brands.
Multiple choices in dimensions, stock design, barrel length and sight options for a variety of shooters and purposes, instead of a one-size-fits-all approach leading to shooters replacing everything but the action as is common with some other brands.
An emphasis on taking rimfires as seriously important to their companies' reputation and bottom line as a dangerous-game rifle or military side arm.