I loaded in around 100k rows and performance was fantastic.
I think the only feature so far I haven't found is whether there is a way to join tables together in the app. With SFDC particularly it doesn't seem to have an option to write the SOQL query directly, and I can't access relationships with the field builder, so I have no easy way to do a client side join (apart from a ton of VLOOKUPs which is not ideal)
I do love how calculated columns stay even after I re-query the source data, that and the auto-expanding are killer features.
Super exciting product, very polished, I can't wait to see where it goes.
PS. $18/mo for the pro version with scheduled queries is an absolute steal