A spindle lock makes the changeover quick and easy. A shaper and router in one machine. Because of their low cost, router tables have become the popular choice for shaping in small shops.
Routers have other advantages, too.
The small diameter of a router bit allows you to shape tight contours where a shaper can't. And you can buy several router bits for what you'd spend on one shaper cutterhead. But the largest router is no match for the versatility of a shaper. The spindle of a shaper will reach higher than a router bit to shape profiles on wide or thick stock. And unlike router bits, shaper cutters can be inverted, which reverses the profile, giving you more options.