best value we have found is the EVO4s with a G dash. 5 analog Chanels plus RPM. Can add more channels (4) with Chanel expansion. We generally log A/F, Fuel Pressure, Fuel Level, Oil P, water temp, Brake pressure, steering angle, TPS, RPM. Or for a bit more money we go with a MXLII adding the expansion cable.
The solo is great for just starting out but will not expand to other sensors. it does work great for stealing other peoples data.
The gain for a Smarty over a GoPro is it works. Turns itself on and off from data command.
Yeah the Smartycam is expensive but worth it IMO. It's essentially a data system itself. At times I find reviewing Smartycam video with speed overlay to be more useful than graphically presented data. With graphs you often wonder or have to look deeper as to why you might have been faster or slower on a particular lap or corner. With video you can often see it very quickly. Mine is more than 10 years old, has been repaired once but is one of my favorite purchases.