the problem is that you are using the TotalWeight Column. The total Weight colummn is calucalated as Weight * Quantity.
if you have 2 1lb items in the cart, the totalweight is now equal to 2, not 1.
use the weight column instead.
$totalShipping += (($this->ConditionalTotal("Quantity", "Weight", "1") * 0.50) - 0.50);//Result
also, for the Base shipping and handing chage, set the trigger to be:
number of items with a specific column value:
If the totla number of items where 'Wight' has a value of '1' is '>' a value of '0'
and set the charge to a flat rate of 5.50