It is quite normal to start with small groups for economic reasons. If the first results look promising, you can scale up. If they are a wash, you haven't spent too much money on chasing yet another placebo.
The problem is that invasive novel treatments like this always have a large placebo effect, so not doing a placebo controlled trial is essentially a waste of time and money.
Not just economic (although it definitely ties into it) -- finding an eligible patient population also another complicating dimension.
Also an opportunity to further design or evolve the study.