(just a coincidence the same name as James Killen pga ?)
depends to a certain extent what metrics you most interested in looking at - but for that to be of real help then you also gotta have some knowledge of how it relates to golf swing motion of the individual & the club
personal launch monitors (not cheap but relatively affordable against $18000 for gcquad & $25000 for trackman 4 approx price for units but then you have yearly license fees on top + golf simulator)
I got to use a friends Zepp2. What i will say it save your £120 on it or anything else like it in the market and get a block of lessons with a PGA pro.