Some tandems the heavier child sits in back; you can look around. Also, I started putting my younger tot in front at 8 months, anyway. The baby preferred to see well, and the toddler preferred the rear, comfy seat. I have a tandem because we do a lot of walking and I don't want to have to ditch into the road at every stretch of narrow pavement, or struggle to get into little shops. Graco tandems (Argos does them) are all pretty good quality. I tried buggy board, but not workable if you walk miles like I do.
A friend bought the MacLaran side-by-side; I think it's a lovely stroller (I think all the MacLaran's are great), but impractical for how I live. When her 2nd was 3 months old, friend also bought the same tandem as me (Graco Duo Deluxe Travel system), when she saw it, because she got so stressed at screaming from her infant, who couldn't see mummy. I know she appreciated the Graco very much, but I think she went back to Maclaran within 6 months because it is lightweight and easily folds to fit in car, etc.
We go to street market and put 25kg potato bags on the tandem, with 3yo sitting on top. Buggy creaks, but gets spuds & kids home. You can't do that with a side-by-side!
Hope that hasn't confused you more...