Or some other options:
1. buy an MSX2 or higher with 128kB built in RAM (or more)
2. buy a RAM expansion cartridge that works on MSX1
3. buy another SD-card expansion, which includes RAM (like MegaFlashROM SCC+ SD with RAM or Carnivore 2).
With just MSX1 and no subdirs, the SD card thing is useless, as you can only store 112 files per partition....
I think option 3 is the best 
.
I think option 1 is the best, because you wouldn't want to miss out on all that great MSX2 software that is around... or combine it with option 3
I think the SD-512 is inexpensive but also limited, because even though it does have MegaRAM support, it can not be used at the same time as the RAM memory mapper. This complicates things on computers with less than 128K because you can not use DOS2 at the same time as the MegaRAM function (at least that’s how I understand it).
In the 90’s / 00’s I would have loved to have the SD-512, just like I loved having the Sunrise CF-IDE, but nowadays there are better alternatives even if they are a bit more expensive.
Sure there are a lot of more expensive and better devices, and yeah, mega ram you would be needing to use DOS1 and FAT12. Not sure about the cost on other countries, though, here in Brazil you can have a 512KB SD Mapper for USD 70, while a mega flash rom SCC w/ 512KB will costs 139 EUR + Shipping and there is a great chance of having to pay import taxes, which would then be 220 EUR + Shipping...
If someone just wants to quickly load and play MSX1 rom games and most of then work fine without SCC and/or a Konami mapper, at least in Brazil, the difference in price is quite astonishing... Almost 4 times the price if you have to pay taxes, if you are lucky, 2.5 times the price...
In general my preferred device would be to go all out and have a GR8NET or a Carnivore along with a MSX2 or a 2+, but some times and some regions budget constraints might change that for other options that in other regions might not look so appealing 
