I have used it on quite a few projects, i like it, projects were successful and i'd definitely use it again
Some things i found
You really need an S7 300 Cpu with an ASI Master to properly diagnose the Asi safety monitors/bus ( I am talking a siemens job here only as i haven't used other makes ). Siemens state the 200 can do this - Its not easy and doesn't work very well, the 1200 doesn't support ASi directly either.
The safety at work software is really quite easy for setting up the ASi Safety Monitor/s
As said above limited to the number of nodes, 64 from memory
And one thing i dislike is if the ASi Safety monitor fails (siemens ones) then you have to fit a new and go through all the teach and setup again, would be better if this was stored on an eeprom or card that can be unplugged and plugged into a new unit by maintenance
The plus side is the site time in wiring, saves a lot of time just running out the yellow and/or black asi cable rather than hardwiring every safety device. Erm does the labour saving off set the ASi cost - In the jobs i have done thats a definate yes. All the jobs i have done had digital IO, Analogue IO and Safety IO on the same ASi network. Length isnt really a problem if you use repeaters and extenders with an end terminator, although if you stick to the standard 50m (FROM MEMORY !) then none of that is needed
If you havent done ASi before and are proficient then read the manuals and all the info on the ASi sites, if your arent proficient then take a siemens course, they are pretty good.
http://as-interface.net/
http://www.as-interface.co.uk/
http://www.automation.siemens.co.uk/main/business groups/communications/asi/
If you get into ASi then invest in the ASi sniffer (Siemens and others do it) and a decent node setup and diagnostic device, i think mine the gossenmetrawatt one and its far better than any others i have had the pleasure in using
And as mentioned above i also use the sick safety lasers with the associated sick asi safety node - very very nice kit and software for the lasers is free