Yup, I've only ever burned BD-R SL (single-layer) discs of 25GB from MediaRange. It's not of my convenience though as bigger discs would have been better for my needs, it was because of the pricing BD-R DL and XL have at local retailers.
One BD-R XL of 100GB disc here is 11$ with shipping, while 4 BD-R discs of 25GB are 2.30$.
As for how I've burned them, unfortunately I didn't use the method above even though I had between 15%-16% free space on all discs, didn't knew about it until today. Now I hope I won't have dead sectors if I verify the discs an year later...
Well, I have 34 more discs left on the spindles so I'll keep using the same settings as now, and after I get more discs I'll use the method above even on these 25GB discs. As writing speed doesn't matter much for me as it matters to keep the data as error-proof as possible.
These 100 discs I'm burning now will be used as reference and research material in case one fails the verification or starts roting in a few years from now, so I need to keep the burning method the same until I'm done. Especially since my discs are (CMCMAG-BA5-000) and are known to be low quality from what I've read. So information about how they age in time will be precious on the internet.