i have made the same experience, with restorer.
1. your ship is less on smoking then without restorer
2. you repair not faster BUT earlier
3. you could repair higher
i.e.
20k DP
no restorer - after hit and smoking - repair to max 16,5k DP
with resorer - after hit and smoking - repair back to 19k DP
so. with restorer i will repair earlier and got more DP after that.
my setup for all nations is..
1 BO
2 Maingunners
5 Engineers
4 Repairer
1 Restorer
1 Scout
If i play with second pair of Gunners (AA/HH) i use 4 Engineers and 3 Repairer.