Yes, you can use the obel with no buffer but if you use the onboard switch you will have signal loss on the effects loop side with the added cable. You can eliminate the switch and just use a 14b jack, see Jerry's Travis Bean 500 wiring. But on that note, effects with buffers will intermingle and produce a tone difference of your old clean signal as they will always be in the loop. I believe that is why Jerry put the buffer in. Ymmv
Disclaimer: I make and sell Buffers. I also sometimes Modify, Build and sell preamps and amplifiers. My opinions are not intended to be sales pitches. I am a one man shop and prefer to spend time with my wife and family, i work full time on call and love to spend my spare time doing other things. I only make, modify or build things for those that seek them.