I'm not sure where you are getting this information. According to the MemSQL documentation, they have one and only one isolation level, READ COMMITTED. But READ COMMITTED takes write locks and blocks reads, but doesn't take any read locks. Blocking behaviour still (and should!) still occur.
It sounds like you are looking for dirty read behaviour, but from the literature MemSQL doesn't support READ UNCOMMITTED.
Update: Read a later FAQ on the MemSQL website. They are using MVCC, so write locks are irrelevant. My apologies to the MemSQL team.
It is addressed in this FAQ: http://developers.memsql.com/docs/1b/faq.html#c1-q4.
I didn't realise you had a new FAQ up on the website - I'll have a look.