Howdy.  I have used 2 SyQuest EZ135's and a SyJet (1.5GB) on my A1200s and had problems with all of them (all scsi).  I had to use an A500 to format the EZ135 disks because the 1200 wouldn't do it.  I don't remember about the SyJet.  The performance of one EZ and the SyJet were always spotty.  I don't know the difference between the successes of the two EZ's.
The weird world of SyQuest.