What is your experience with EcoBreeze sheets?

I got a sample pack of EcoBreeze detergent sheets with my grocery order the other day. I've been wanting to try them, but haven't committed to buying them because I was worried they wouldn't get out work clothes clean, husband and I both work dirty jobs. I tried the sample last night and used a full sheet on a load of work clothes. It seemed to do an ok job, but the next load I used another full sheet and added some borax for a little extra boost, which is my normal routine. But when I was folding the loads that had the borax added, I noticed that some of the clothes had gunk stuck on them, clearly from the sheets not dissolving properly. I had this issue with pods, so I haven't used them since. I have an older (maybe 10 years?) Maytag front loader, set my wash setting to between warm and hot, extra heavy soil setting. I was pretty bummed because I really wanted them to work. Wondering if anyone else has had this issue with the detergent sheets? Why would borax make it not dissolve properly?