It all depends on what you want the CBD for. The advantage is you can mix your dosage to suit your needs instead of buying a pre-mixed oil or vape fluid which may be too strong or too weak, you can easily dissolve them into the likes of olive/coconut oil or shea butter to make topicals, dissolve them into butter and make edibles, basically the advantage is the ease and versatility as you can warm up and mix 1g of crystals with 0% nicotine e-juice base and there's a 10% vaping fluid, warm up and mix with olive/hemp/coconut oil and there's the drips to go under your tongue, make your butter for edibles, etc, etc, etc.
The price isn't too bad when you consider the price of the likes of the Sensi Seeds e-juice, the rough figures work out at £36 for a 200mg bottle, or 2%, so the smallest pack there would make 10ml of e-juice at 2.5% for under £20 given the cost of the base. That means the savings are kinda obvious in that respect, even including the time and energy needed to slowly warm up and mix everything in a "bain-marie".
So it all depends on your needs and what you want to do with it, as sometimes a premixed oil will come in cheaper (I know how much I pay for 5%, I can buy two bottles of oil for the price of the 500mg crystals), personally that would be made into e-juice within minutes of me getting it.