Group: Forum Members
Good tips above, but just to add one:
Put a lot of effort into pressing down your bagging tape.
I think until you realise how tiny a leak has to be to cause problems, you won't realise how much effort it can take to get the bagging tape to seal. This is especially true if you are using a firmer or older tape, there are many different grades and some are much easier to get a seal with than others. But even the soft ones can often take a lot of pressing to fully close a tiny air passage, and if you try to take a shortcut and not work every inch of your seal, then there's a good chance you will miss the leak. My thumb nails will often feel bruised for days after an infusion, that's how much effort it can take.
It is finicky stuff, sometimes you can throw the bag on and barely put any effort in and pull a 100% vacuum straught away, and sometimes you will work and rework every inch of the seal 2 or 3 times and still have a leak, and it's only on the 4th time around while your thumbs are screaming for mercy that you magically press the right spot and the leak is gone. Following beliblisks tips will improve your chances of getting a full seal without the pain, but if you've done all that and still have a leak, you're better off spending your time working the bagging tape than you are searching around with a leak detector.
To answer the original question - I've got a Bacharach Tru Pointe 2100. It was hideously expensive, it works well. It has probably paid for itself by now, but I do this every day and have been for 8 years. I would estimate it has probably found 1 in every 25 leaks that I have had in that time. For the hobbyist, those aren't great numbers. Ultrasonic leak detectors are ok, but I would consider them luxury equipment for the professional rather than essential equipment for everybody. Nail your technique and put time and effort into the bagging tape, and 24/25 times you won't need the expensive gear.