I used the SLA quite a bit last year. Caught 2 of my 3 biggest fly-rod fish on it. Never had a problem with it at all.
The Allen & Co XL, to me, actually feels a bit more solid and sturdy. The XL looks very similar to the SLA, but isn't identical.
The vests/packs appear to have many of the same features as some of the Fishpond offerings.