Hi, Main advantage for me with ASR25 vs. ASR35 it was half price at time of purchase and it is much more compact. When it comes to Dust Class L vs. M, I wear M class full-face mask and ear defenders on every job when I am using wall chaser. If your budget allows, go for ASR35 as it is M class more suitable for concrete and brick dust extraction, but you still have to wear suitible PPE.