I have only used tempered glass protectors for awhile now, as I believe they offer the best protection for the price. My Go-to brand is Sparin
Very high quality/customer service. The reviews in the link may not indicate this but it appears 2 of 6 got the wrong version, which was quickly correct in the first instance.
I do not have an E4, but have them on MXP, X2, G5+ and could not be happier…(when I gifted the X2 after years of abuse, the screen was in bad shape, until I removed the cracked and broken, scuffed Sparin protector to reveal the pristine X2 screen).