The highest recorded espresso temperature was a little over 197° from the bottomless portafilter. The lowest temperature, 186°, came from the metal double-spouted portafilter. This represents an 11° difference.
The absence of spouts in a bottomless portafilter eliminates dripping, making cleanup easier and more efficient. The open bottom also allows for easier rinsing and wiping of the basket, preventing coffee oils from building up and affecting future shots. The extra space underneath also improves workflow by accommodating larger cups and eliminating the need to transfer espresso.
This video by John from Whole Latte Love explores the benefits of using bottomless portafilters for espresso extraction. It covers how they help identify channeling issues, provide extra space for scales and larger cups, and impact espresso temperature.
The video states that channeling can be caused by a number of factors, but the one most easily controlled is puck prep. Issues with puck prep could include uneven distribution of fines, inconsistent tamping, or a lack of techniques to promote even water flow. Additionally, a poorly maintained grinder (especially an older one with unchanged burrs) can also lead to bad particle distribution and result in channeling.