The SOK is a great deal for a heated battery as its only $1000 shipped from there site and has heating, just not good if you are using it on a boat because its metal:
https://www.us.sokbattery.com/product-page/12v-280ah-lithium-battery-built-in-heater-and-bluetooth
The SFK is smaller in size and I usually tell people to get the kits and save $ but recently hardly any difference in kits and pre-built as the coupons only work on pre-built.
Looks like they have some reviews of the 275EX out:
I like it but now the pricing on the kits make no sense as they are only $75.00 less with coupons so I'm hoping they don't start doing this and lower the price of the kits.
I think love your rv is reviewing the 300 but his is going to be a multipart:
A guy near me has 8 sok sever rack batteries and 4 of the 206 in his camper and he says he loves them. I have 2 of the SFK 3.5 kits and I love them as well so both are good brands.
In the end if you are going to use victron or need some of the advanced features go with SFK but if you just need a good reliable and want to save $ one then go with the SOK.
On a side note I don't recommend any of the el cheapo stuff like Wieze or Chins, I tell you these batteries after a year or two never charge higher than like 12.9v because they have become so out of balance.