Can I use these to just connect my turntable to my receiver?

Yes you can and you'll be pleasantly surprised!

will it work for my speaker and subwoofer？

Hello Paula, It will works without any issue if you have the device with 2 RCA males to 2 rca males, The quality will be fine with them, rest assured to purchase. Thanks,SKW support team

Do i understand this correctly that these cables are digital cable and not suit for analog connections. Wondering about frequency spectrum

Someone might use these to carry a digital signal (i.e. coax) in a pinch, but RCA type interconnects in this configuration are generally used to carry analog stereo (L+R) audio. As for cable snake oil, you can consider this one completely transparent for reasonable use.

How would people describe the sound compared to other cables like the slightly more expensive Bjc LC-1?

Impossible question to answer without having both sets of cables to compare. I sold audio/video equipment for 20 years and have found that sound comparison questions can be answered in one simple way..... close your eyes and choose which sounds best to you, the cost is irrelevant.