Its not all about driving slow; its about conserving momentum. People say that an ES1 Civic w/auto transmission can't get more than 10 in local, and 13-14 on highway without A/C. Check my signature; keep in mind that this was a 270k driven car, running on 20w-50 oil. Ambient temperatures were also quite low, which is bad for fuel consumption.
BTW, xcel of cleanmpg (Wayne Gerdes) has a lifetime average of 21 kml on his K24 automatic Accord. On highways, he can maintain up to 26 kml. Whoever says that driving style doesn't affect fuel consumption is not really trying.
Don't waste your time or money on these. Get a good 0w-20 or 5w-20 oil and fill it to halfway between the marks on the dipstick. Pump up your tires to what is written on the sidewall, probably 44 or 51 psi. Start just by following the speed limits and shutting the car off on signals. Accelerate and brake gently. When you are satisfied with the results, you may want to move on to more advanced techniques; check out the link in my signature.