Early on in my quilting, I bought the June Tailor HST QST ruler from Joanns, which works well for simpletons like me who often have problems with visual cues - you can easily see if you are centered properly for both cuts and whether your blocfk is a bit short of the mark. However, if you are doing non-standard sizes, it looks like the Martingale is a good bet. I have seen the block-lok's but I don't know if that little lip thing is worth the dough.