Comparison of tier 4 vs student visitor visa

[Uberdude]

A little background: I am a UK national (28) with a Thai girlfriend (27); we met in Korea last summer, I visited Thailand in the autumn and from October 2013 to March 2014 she was in the UK with me on a general visitor visa that I sponsored (I wasn't working at the time but have lots of savings). She's back in Thailand now and wants to do an English language course here in the UK, staying with me (I'll pay for the course and her expenses).

I thought that a student visitor visa would be the appropriate one for this, and that I would be able to sponsor this in a similar manner to the general visitor. My first query is about sponsorship: on the old UKBA website there was information about this for the general visitor visa but not for student visitor, does the concept exist for that visa category as well? The new gov.uk website is rather lacking in information about sponsoring at all (other than saying "you must prove you have enough money to support yourself without working or help from public funds, or that relatives and friends can support and house you").

I have read about some guideline (is it a strict rule?) about not being allowed to use repeated visitor visas to stay in the UK for more than 6 months in 12. Does this only apply per visa category, i.e. no general visitor and then another general visitor soon after, but general visitor and then student visitor 4 months later is ok, or is the latter case not allowed too?

My girlfriend has spoken to various school/visa agents in Thailand and they all seem to agree that a tier 4 student visa is better and more likely to be approved. That would require me transferring about £5000 to her account in Thailand to show she has the funds to support herself rather than me acting as sponsor (she doesn't have the money herself). I thought the tier 4 was harder visa to get (and usually used for things like university degrees rather than short English courses), or is the idea that if you meet the tougher requirements (and pay a higher visa fee) you are more likely to get it granted. Seeing as a large deposit like that needs explaining that it comes from me, how is that better than me acting as a sponsor? (It's now her money so if we break up she can still support herself? showing I trust her?) The Thai agents seemed to give the impression UKVI is keener for foreign money to pay for the course fees / living expenses of foreigners in the UK as it's helping the UK's export figures / balance of payments. Is there any truth in this? And anyway in reality of course it does nothing to help get foreign cash into the UK as I sent my sterling out to Thailand before bringing it home minus bank fees and exchange rate loses.

Many thanks in advance for you advice.