The ground they're moving to is in a much better location. It's far closer to Manchester city centre, Salford precinct and the Willows than the AJ Bell is, so it's likely to be closer to where the majority of their fans live. It's obviously not as handy for away fans travelling by car or coach, but it's better for those travelling by train.
I've always thought the AJ Bell was perfectly located for Sale (if you ignore the fact that it isn't in Sale obviously), because they have a more widespread support as "The North West's team" in RU. A far higher percentage of their crowd is likely to be driving to games from 20+ miles away, so a ground with motorway links suits them.
Salford are a community club and their fans are mostly going to be people who live in the area and are more likely to want to walk or get the bus to games, drink in local pubs etc. The football ground is in a better place for that. The 5,000 capacity does seem worrying though. It's all well and good saying packing it out will create a better atmosphere than the AJ Bell, which it will, but it's not right for Super League is it? Unless they have genuine plans in place to expand it quickly, which I highly doubt, they're inevitably going to drop to the Championship eventually, and not be seen again in Super League for a long time once they do.