Leica SF58 TTL or Nikon SB800?

Hello Dear all,

I would like an advise about a flash for my Leica M.

I am planning to buy a flash and use it with a off shoe cord.

I didn't find much information about the SF58 on the internet, except people saying it is overpriced and it is a copy of a METZ flash.

As I understand so far, as I am new to flash use, the SF58 is TTL so it means It can measure the light via the M body and the flash will get the proper exposure.

If I do not want to use it TTL, does this SF58 work in A mode too? Is there something on the flash itself to measure the light?

Then, I found threads where people use Nikon SB800 on Leica M. It do not have TTL, but as I understand it can be used in A mode. Basically, the only difference between the Leica and the Nikon are that the Leica has TTL. They are almost same price but I've also heard the Leica flash is a bit harder to use properly.

I would like to know if some people around here have both or one of these flash and what are their suggestion/experience worse sharing with them to help me at decision making.

Michel