I have both, slx and phoenix, also a clx,
I find the phoenix much easier to use for 3 main reasons, the clamps are so much easier to operate and much much faster, they don't get caught on any guttering etc
The diameter is much thinner than slx poles, I find the grip and feel is more ergonomical, and less tiring,
The phoenix brush recently released is absolutly brilliant, very light, great scrubbing power, and excellent splay on the glass, seems to always work better than the super lite.
However, the quality of the gardiner slx range is better, by a long way. If facelift upped there quality standards, I would say they would potentially out sell gardiner poles...
I still highly rate gardiner, but for me, the phoenix seems to get the most use daily, I naturally gravitate towards it for ease of use. It won't last as long as a gardiner pole mind!