We are very pleased with the T12si! It took me 2.5 hours to unpack and assemble. The kit comes with allen keys for assemly but you will also need a phillips (crosshead) screwdriver, a small adjustable wrench (or 9/16" spanner) and something to cut a couple of plastic ties. It also mentions you need a pair if slim nose pliers and a mallet but I did not find these necessary. As an aircraft engineer I did not have any difficulty assembling the treadmill BUT I would think some would struggle. I would also recommended it is assembled by 2 people! We purchased ours with an IFIT Weight Loss Level 2. The 1st level of this programme is not for the faint hearted as I found it a pretty tough 30 minute work-out and I consider myself reasonably fit. This is probably because it automatically adjusts the incline as well as the speed throughout the workout and this really makes you work hard. It all makes for a very interesting workout though it may take some members of the family a few weeks to even manage the 1st setting on the IFIT 2. But even if you feel that the IFIT is working you too hard, you simply press the incline 0 button and the treadmill returns to level, or alternatively simply press a button to select a slower speed - it is that easy! Please not that I read another review which said that IFIT 1 was too easy and that there was a very big leap from IFIT Weight Loss 1 to IFIT Weight Loss 2.
We love the T12si!