I use the glm 20, it does a really good job for almost any interior measurement and at 4" X 1" it is so small I often forget that its in my pocket after an inspection. Since the glm 20 is only good up to 65' I keep the glm165 in my appraisal case. They both use 2 AAA batteries and I prolly have to replace the batteries 3 to 4 times a year, the batteries would last longer but I like to watch the cats chase the red dot. $30 (nib) on Ebay with free shipping, buy 2.just looked at it. the glm 20 model is about $100 less. but i do like the brighter, larger numbers on the screen. the only aggravating part is always finding the red dot in bright sunlight. they are good for indoor measuring. i will pay more to have less aggravation, even 5 seconds less. i also like that it is thinner than the 20 model. i think i am talking myself into getting it. doesn't hurt to have a spare.