That spinel is purple/gray. If that is what you were looking for, I would go for it. Otherwise, I think that a kashmir cushion would be as close as you could get to replicating the original photo you posted
This type of question comes up all the time and it really depends on what you are after. If you are going for "the look" and have no issues with lab grown stones, you are NOT going to be able to get a more beautiful blue stone (IMHO) than one of the BTD sapphires, especially for the price.
Having said that, I'm an earth-mined stone junkie now, so I buy earth-mined stones for my rings, even though I own a couple of BTD sapphires. Are the earth-mined stones prettier - no, but I love earth-mined stones for their uniqueness. It's a very personal decision and there is no right or wrong as far as earth-mined vs lab grown.
As far a spinel vs sapphire, it is next to impossible to find an earth-mined spinel the same color blue as a sapphire. If you do, you will discover that they are quite pricey. As others have stated, blue spinels almost always have a tinge of gray to them in some lighting (often referred to as steely). Some people love that look, but if you want blue blue, a spinel is going to be tough to find in that color unless you are willing to shell out a lot of money.. Also, a spinel (although a great stone for a ring) is not quite as durable as a sapphire, so you might want to consider that also.
As far as the seller of the kyanite saying that those stones are often used as a substitute for sapphires in rings... uh, NO... for the reasons that have been stated here - not durable enough for a ring IMHO.
Tanzanites are gorgeous, but are have to be babied a bit, as they are not as durable as a spinel OR a sapphire.