I am of the opinion (which may well be wrong, as I don't know what difference there is internally to make them 'better') that a coil either works or it breaks down and fails.....
....now, I assume that a £70 coil will have 'better' stuff inside, and so will take more use/abuse than a 'cheap' one.
However, as the 'cheap' ones are stated as being "OE Standard", and thus suitable for use in many types of GM cars of the era, that they will work as well in an Elan as any other such item, for as long as it works!
Now, as the originals in my project are 30+ years old, and have taken the car a smidgin under 80K miles, I have no way of knowing just how close they may be to failure (I put MSD on the green car when it had 130K miles on, at 15 years old - and the same on the red car).....
..... so I intend to fit my new (cheap, from Rock Auto!) coil packs whilst the current ones are still working, thus I expect them to last a while, and I will retain my old ones on the shelf in case of an unforeseen failure, which means I can stay on the road until some more new ones arrive.
Unfortunately, I lent one of my old sets to an ex-member on this site who fitted them, decided they worked, promised to get some new ones and return mine, but then sold his car and promptly disappeared and failed to reply to communication
The other old set was kidnapped by the ex-wife of a member who held them to ransom along with a set of my injectors.... and I had no intention of bowing to unreasonable demands, so chose to write them off and get on with life.