The phrase "is useful as a" is grammatically correct and can be used in written English.
Example: This pen is useful as a tool for writing notes during meetings.
When the extension is used without the shoulder rest it is useful as a guerrilla gun, (i.e. hide and shoot then hide again).
This strategy is useful as a tool for monitoring immunity following vaccination and can also be used to define relevant epitopes for the creation of novel vaccines.
7 Sulfur, used for acne since the time of Cleopatra, is useful as a drying and antibacterial agent.
That said, the NSS is useful as a benchmarking tool.
It is useful as a food for canaries.
Nitric oxide is useful as a signaling chemical because it easily crosses cell membranes.
And marginal productivity theory is useful as a rough description of how relative wages are determined.
"I hear you as skeptical about whether consciousness is useful as a scientific concept," another researcher ventured.
He says that being 'funny looking' is useful as a character actor; it allows flexibility and also credibility.
Some proponents argue that whatever the freestanding authenticity of the cross-discipline, it is useful as a carrot to attract indifferent students.
As with all experimental electronic music, the addition of images is useful as a means of bringing the sound to a place of emotion.
