The neat little Flightsketch mini altimeter is a very impressive little altimeter and is worth the price of $40.00.
I tried one out on the Quest duel motor cluster kit called Magnum. The little altimeter provides not just the altitude. It also provides wind speed, temperature, and humidity. You can upload it to their web link and review the data as well as download the CVS file from the site for record-keeping: https://flightsketch.com/flights/1158/