The complete LED Retrofit trim has many advantages over the bulb replacement.
What is Kelvin?
Kelvin temperature is how they measure the color of the light your LED bulb puts out. 2700Kelvin is often compared to your standard light bulb color. Keep in mind that when you dim a standard light bulb turns more orange while an LED's color will stay the same as you adjust brightness.
What color do you recommend?
Color tempurature is largly a personal preference. When asked I often suggest 3000K it is a bright light that makes things like artwork pop without looking too harsh.
I saw an LED trim at store xyz for less, why are yours more expensive?
Not all LED's are created equal. You often get what you pay for. I will not install LED's with a CRI of less than 80 and a life shorter than 25000 hours. It has also been my experience that the higher quality of LED's dim better. Many of the lower end ones are not dimmable at all.
What is CRI?
CRI is color Rendering index. It is most directly a measure of the quality of the light produced with 100 CRI being the max. Shy away from any LED with a CRI of less than 80.
The LED says it is dimmable but it won't dim.
Many LED's say they are dimmable but you must also consider if the LED is compatible with the dimmer. This can get to be a complex subject. A good resource is Lutron.com/ledtool.