+1, We noticed to issues while using the two plugins, for us:
Jenkins: 1.446
Config slicing plugin: 1.28.1
Email-ext plugin: 2.16

First issue was that the Slicer only was modifying the default setting (which we do not use, we use the Failure case almost always.)
Secondly the default subject and default content was not filled out by default. We started to get a ton of e-mails with no subject nor body. After consulting with the team we realized we'd recently made these changes using the slicer and they were not being filled out.