The fuse also compresses the spring a bit, so it may not be quite as safe as running it the way Robert built it. The spring works, yes, you need to have some spares around, but I've never lost one yet. "Measure twice, vape once", i.e., check, check again, then check one more time before you hit the fire button. Check the resistance (ohms) when you build it, check it again when you're done building it, and after putting on the cap and taking it back off, then check it again after you put it on the REO.