[SpartanTau]

PATHFINDERS
Good:
- Great source of Markerlights for a reasonably low cost
- good weapon selection (Pulse Carbines, Rail Rifles)
- compulsory Devilfish has a Marker Beacon (allows more accurate Deep Strikes)
- able to fire Seeker Missiles
Bad:
- very immobile if Markerlights used
- expensive when combined with the cost of the Devilfish
- vulnerable to enemy fire, especially template weapons
- easily disrupted from doing their job

Recommendations:
Equip the necessary Devilfish as a Warfish. This allows you to get some teeth with your Markerlight investment. The Pathfinders should be deployed in cover, or if this is not possible, right near some. The Scout move can then be used to take them into cover, giving them much needed protection against Heavy Bolters and the like.
If you are using Rail Rifles (which should be rarely), take them in either a squad of four or six. This gives you a good unit for a lower cost, especially since the rifles almost double the cost of a single Pathfinder. They shouldn't be used in battles of less than 1500 points, as they are an expensive investment that usually don't benefit armies in lower point games.