tl;dr They found that it was effective for working memory over 9 studies, with non-significant effects in other domains.
Cool. I wish the machines were more affordable though.
There are cheap devices on the market. However I reckon previous studies were all against any effect on TDCS.
I do have a device, tried it, won’t notice the difference
For those interested you can get a tdcs machine for $77 (£60) on ebay: