I did an 8 week run of Osta in2015, 25mg for 8 weeks. My blood tests showed a minimal drop in test, so I figured it was just fluctuations. Then I did an Osta run in 2016 and I posted my log with bloods on here at the time. My test levels dropped from ~550 to ~125 with 10mg for 12 weeks. I just used BLR Rebirth for PCT for 4 weeks and it brought my levels to ~450. At that point I was fine letting my levels come back naturally. Three years ago I decided to do a long run and ended taking 10mg for 2 years continuously. Again my test levels went from around ~550 to ~125. I did a PCT with Nolva for 4 weeks (20-20-10-10mg) and my levels again were back up to ~450, but with LH slightly elevated (which I guess was from the Nolva). It's been a couple of months since the first test, so I am about to do another blood test to see where I am now.
Bottom line, Osta does suppress you, but it doesn't shut you down, so you can recover relatively easily. I would recommend doing a PCT with Nolva, but most of all I recommend doing bloodwork so you know exactly where you are.
As far as whether it works or not, it depends on what you want. For me, I could workout like a beast three times a week and be recovered by the next day, no muscle soreness, no joint achiness. At 50 my body looked as good as when I was in my 20s, lean, buff, and mahogany wood. So yes it works. if you are looking to get massive, then it's a very steep ask.