Is your daughter at least one year old?
First, I will mention that rear-facing convertibles can be installed more upright than infant seats, so they often don't take up any more front-to-back room. You also could install them in the middle with the lap belt. So if you just bought the CarGo, you could return it and try a convertible.
Second, I'm not sure if I understood your post correctly, but your daughter is using it with the harness, right? Because she is too little to use it as a booster with just the seat belt. She would need to be at least 30 pounds and 35 inches just to meet the seat's requirements, and it would be better to leave her that way until the maximum 43 inches or 40 pounds.
Of course, if you're daughter is over a year and you're sure you want her forward-facing, the CarGo is a fine harnessed seat. I'm not sure how heavy it is, but my very plain Ultra CarGo is nice and light, so I think it would be easy to move around. You can install it with a lap belt only IF you are using it with the harness, although you always get better protection with the tether. (You CANNOT use it as a booster with just a lap belt.)
I think your daughter will stay harnessed in the CarGo for a long time (even a tall girl will last in height to age 4 as long as she is average weight), but I'm guessing once she is too big for the harness you will want a different booster seat. She will probably still need to use the belt guides at that point and threading the shoulder belt through them is not that easy. It wouldn't be that bad if you could leave it in a car all the time, but rethreading it every time you use the seat would get old fast. So if you like the CarGo as a forward-facing seat, that's fine, but I wouldn't count on using it as a booster later. (It is safe to use if you keep an eye on the tightness of the seat belt.)
I can see how it would be easier to leave her forward-facing. It is important to be able to install it correctly every time. The hard part with the variety of seat belts you will be seeing is identifying which ones lock and how. Here's a good link for that:
http://www.cpsafety.com/articles/lockincss.aspx
It's great you're so concerned about your daughter's safety. I'm sure you will feel more confident after you see a tech.
Julie