True. If you can add a second modem for $50/month, that's slightly better than paying for 300GB of overage fees (300/50*$10=$60/month; is my math right?). However, you would need to use the entire 600GB to realize any savings. If you only need 450GB, it would be better to pay for just what you need. If Comcast offers faster tiers with a larger cap, that might be more cost effective plus it's faster.