The smaller is certainly better than no collector. If you have a good "shoe" for your router, it should work OK.
Of course I am a bigger is better fan, and my collector is 1.5 hp and 5" inlet. I got mine at HF and it has done fine for a couple years now. I added a canister filter in place of the top bag and use a poly bag for the bottom. The filter improved air flow noticeably.