Bearing Blocks vs. Idlers

[MattC9]

Recently I have been looking to chain tensioning systems for drives and I have been designing in a movable idler sprocket into my drive, but recently I have herd that idlers decrease efficiency and take power away from your drive. I would like to run bearing blocks but I think they require a lot of machining. Do bearing blocks require a lot machining, and are they worth the extra effort when it comes to the over all efficiency? Also do idlers really take a lot of power away from the system, where you would want use a lot of machining resources for the bearing blocks?

If you have any other input tips or tricks that you have found while designing something like this I would love to hear it!