John, as we discussed, there are videos out there showing imperically that helicoils work far better than timeserts, are cheaper and easier to install. Have a watch of the half hour video I posted in another thread (yeah sorry, it's not a 5 minute job but the guy does a good job explaining what he's doing and why), helicoils FTW every time. Given you now know my history, I have always used, and will always use, helicoils and this video shows why. I've never, ever had a helicoil fail, pull out, or be hard to install.
Do some research into the two, helicoils will give you rated pull out strengths etc. etc. Timeserts just tell you "well they should be strong enough" - they don't actually give out any figures that they will stand by. Also, note in the linked thread, Glenn @B.M.W Ltd states very clearly "Just a heads up...if you don't insert them accurately the block will be ruined. The head bolts will pull them out. Most motor re conditioners have their own special set ups to do these accurately and even they can get it wrong... ask me how I know", just another precaution.......
As I discussed with you on Wednesday night, do a lot of research before doing anything like this, everyone has opinions based on their experience, some advice given is great, some just needs to be taken with a grain of salt as that person's experience. Either way, helicoil or timesert, there is a chance the block can be damaged.
Again though, this is just my opinion, and, like Glenn, more than happy to give you a call whenever suits you to discuss before you decide which way to go.