Loving-Kindness for Concentration

In meditation, I seem to have great difficulty with the breath. Having some stability and mindfulness, but very little concentration, vividness and sharpness. However, loving-kindness works for me in deep ways. **Is compassion meditation a kind of concentrative practice? How far could it bring me along the concentrative path?** Also, would interspacing anapanasati and metta (e.g. doing one one day, and the other another day) beneficial, or **should one try sticking to one type?**