Teka FlexLinea RS15 40.40 3-in-1 Installation Stainless Steel Sink typically refers to a sink that can be installed in three different ways: as a top-mount (drop-in) sink, a flush-mount sink, or an undermount sink. Each installation method has its own advantages and considerations. The Top-Mount sink is placed into a hole cut in the countertop, and the rim or lip of the sink rests on top of the countertop. The sink is secured in place with clips or brackets.

Top-mount sinks are relatively easy to install and replace, and they can be a good option for retrofitting into existing countertops.  A flush-mount sink is installed so that the rim of the sink is flush with the countertop surface. This provides a sleek and seamless appearance, as there is no raised rim to catch debris or crumbs. Flush-mount sinks can be a bit more challenging to install compared to top-mount sinks, as they require precise cutting of the countertop to ensure a proper fit. 

Undermount Sink is mounted underneath the countertop, so the edge of the sink is not visible. This installation method provides a seamless and elegant look, and it's easy to wipe crumbs and spills directly into the sink without any obstructions. 

Teka FlexLinea RS15 40.40 3-in-1 Installation Stainless Steel Sink is popular due to its durability, resistance to stains and corrosion, and easy-to-clean nature. They are widely used in kitchens because of their sleek appearance and ability to blend well with various kitchen designs.