I try to buy in the same block when the opportunity comes up.
There may be some cons, but I haven't experienced too many. Off the top of my head, they might include the suburb being slow in the CG department, in which case, you haven't hedged buy buying in different areas. Also, if there's a major works levy imposed, you get get hit for both units.
If you know the group and the BC and like it, then go for it. If the suburb is a good one for CG, then you can do well with 2 properties there.
Over time, you might get the entire group. That's an attractive proposition and my objective for a couple that I'm involved in.
You're in a better position than most to know if block is a good one to invest in.
One last thing, check with your current lender to ensure they don't have issues in being exposed to 50% of the block. Many have limits that would necessitate you using a different lender for the second one.