I have a different opinion with regards to aquarium vacuums: I use these cheap battery operated ones by Jeneca (1 on each of 3 tanks; fourth is too deep) -- they work a charm, keep my bare bottom tanks nearly immaculate, save me time, and I don't have to suck on any siphons or use bigger buckets (just 6 liter water bottles for each tank).
And the waste is removed pretty much completely (unlike using a net, where about 1/3 at least disintegrates and goes back into your tank (and by then is too small to net again). I also find my Kamfa attacks the vacuum less than nets, which makes netting waste hard when you're trying to avoid an aggro fish or he's pushing the net around. Another fish might be different though.
Anyway if you do this every day (takes 5 min. or less) before the waste starts to decompose too much, then the impact on water chemistry is in fact very minimal -- my nitrates rarely go over 15 (and out of tap it's already about 8) with weekly 40-50% water changes. On one tank (Flowerhorn) I re-fill with an equal amount of water every time I take out (Arowanas don't like me pouring water into their tanks that way and try to snap at it too much), so his water stays pretty darn clean, as do all his tank's filters.
I've never used the Eheim vac, I'm sure it's way better quality/durability than these, Chinese-made Jenecas, which only cost about $11 usd here (plus batteries of course; they come with a DC plug but I don't consider it overly safe lol). I also don't use the little filter sock (some waste will sift through and escape back into the tank), just the hose going straight into an empty water bottle, easy peasy.
Btw, that little motor has enough power to easily draw waste from my 28" high Arowana tanks, let alone my 22" high (115g) Kamfa tank.
Using these, this is what my canister filter looks like when I opened it to clean yesterday, first time in 7 months (granted it's only 1 X 15" Arowana in a 325 but he eats like a horse, gets fed daily and lays some big ones). The foam and bio-media were clean as anything and the water in the canister is as clear as some people's tanks:
Nothing wrong with just using a hose/siphon/bucket, but I personally find these much easier, esp. if doing on a daily basis.