I guess you are talking about the "up to 60%" bonus:
https://buymiles.aa.com/en/buygift
I am passing on it but who knows if the selling miles philosophy will more closely mirror US (cheap sales frequently) or AA (expensive sales frequently).
It is not bad if you need to top off for an award....just be aware the drop-down price is the base price, but then you have taxes/ fees on top of it (ex. the $2,950 for 160,000 miles ends up being $3,201 for me). Still that ends up a cost of $.02 per mile if you do the maximum (the less you buy, a little less good the deal is).
So, the question is could you get a good enough value out of that (ex. loss of flexibility to use other airlines, loss of earning miles on the flight) and would you use it in the near future (i.e. AA could change their point requirements for awards at any time).
For Coach, I usually only bulk buy miles at about $.0167 each or less...calculated by (900 typical Europe Roundtrip -100 award ticketing fees) / (40,000 AA Off Peak Europe Roundtrip Coach Award+8,000 lost mileage earning).
It gets a little tougher to value for Business because obviously few people would pay $5-10K for a flight....but it is definitely worth some amount of incremental extra value that is very subjective.
Anyhow, I don't need the miles now so will be waiting to see if they offer a better deal....the 2 times last year I bought (US DM) were 50,000 miles for $567 ($.0113 each during the 2 100% bonus "share miles" promotions) and 100,000 for $1,880 ($.0188 each during the many 100% bonus "buy miles" promtions).
This wouldn't be as good as any of those but now that AA and US combined, there may not be such good deals again, who knows....