I tried advanced (7x7) three times, it was quite doable. An obvious optimization would be showing the current sum of the rows/columns. Master (9x9) features negative numbers too, which is quite funny.
Master I've no idea how to solve
Keep fixing digits one at a time with things like parity, e.g. if the numbers are all odd and sum to an odd number, you know an odd number of them are needed. If a total is very high or low, there's often obviously only one way to make it. For totals not quite so high, if you choose the few highest numbers, and by trying ways to reduce the total by the excess, it becomes evident what the numbers are. ("Get your hands dirty.")
Often a row/column contains e.g. two 7s, and you know one of them is needed, but not which until other information comes in. (Having an "OR" label/symbol to mark those would be nice I guess.)
e.g. One of the columns I had: total 46, column is 16,-2,12,-2,14,-2,14,16,1. Eliminate the 1 by parity. I try adding the largest numbers, 16,16,14, which add to 46...and somehow I can see/intuit that there's no other way of making 46, as the -2s can only adjust downwards. So you green-circle the two 16s, leave the two 14s blank, as you don't know which is needed yet, and cross out all the others.