I haven't found any situation where a glide is a disadvantage.
I've used a glide on 1.5" and 2" wands, with both standard and high airflow portables, and also with my truckmount. In all cases it makes the wand a lot easier to operate. In no cases does it leave the carpet wetter. In no cases has it resulted in failure to extract soil.
There's no reason why a glide cannot be used with a portable - all it does is maximise the airflow potential of the setup being used.
In my opinion, any disappointing results with a glide are 100% down to the user. Sealing the glide to the wand is essential, otherwise vacuum leaks will work against you. Otherwise, it's down to poor wand technique and/or the inability to set up the extraction machinery with the proper flow/vacuum ratio

In my time I've seen much more bad wand technique than good. Once you get your head around the science of what's happening where the wand meets the carpet, you've got it sorted
