I like these little “utility boxes”
(Please take note! This circuit will not work as a blend for pedals that invert the signal polarity (or phase). For a few examples of such pedals; the likes of Dyna Compressor/Ross Comp and their derivatives and Marshall Bluesbreaker among others. The symptom of inverted signal polarity (phase) will be significant drop in level when the blend pot is set near its middle position. This is caused by two polarity phases cancelling each other out. If you need a way to control the phase, then you need to address this accordingly.)