I have used thangles and had the same problems mentioned in other posts.
I like the method Bonnie Hunter demonstrated in a lecture on using up scraps. Cut fabric 1/2 inch larger than finished HST. Place the two fabrics for the triangles right sides together. Then use the HST Easy Angle ruler by Sharon Hulltgren. Make sure you have and accurate 1/4 " seam allowance. NO tearing off paper NO trimming up after. Simply press seams being careful not to stretch the bias and piece your quilt block.
Here is a six inch block I made using this method.