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I tried the socket and hammer technique and it didn't work. These springs are hidden and very strong and the angle is too sharp. It worked magic on a honda GL1100.
But then you need to put the things back together, which can't be done with a brute force puncher. At the end it has to be securely compressed. I would love to see this tool in action. Says remover and installer, but I can't see it doing the installing from the photo...

I've used the plunger type tool many times for removing and installing the keepers on various motorcycle heads. It's way faster than the C clamp, particularly for installing the keepers, and the real bonus is that it can be used to access the valve seals without removing the head.

PS: With this tool, you don't use a hammer.

I used the C clamp (see pic) - important to get the type with the "tube" type clamp. Some of the OHV types have a fork ending which does not work for an overhead cam/bucket follower design like the 1300. The head needs to be removed to use this tool but probably worth checking and lapping in the valve seats at the same time.

I have a set of valve-stem seals ready to go in this fall. NOT removing the head! Thought of something like this and of course found that someone already did.
Goes without saying, I'll make one. My idea is to make one tool long enough to cover three valves with one bolt-down, so basically four moves - three exhaust/right, three intake/right - three exhaust/left, and three intake/left. I'll get each piston per seal @ close to TDC, stuff the cylinder with some heavy Dacron Parachute suspension line and rotate crank to stuff the cord up against each valve to hold it in place.

A few options to consider!
Scotch, I have this type of tool bookmarked and have been thinking of making one myself. It is a straightforward idea. My problem is not having tools to make it. But I think the is definitely a good direction.

The C-clamp, there are a few on eBay for about USD20. I am not sure which one to pick, and it takes the shipping time from China. Don't want to end up with a wrong one.

The 'plunger' sounds intriguing so say the least. I will look for a video to see it in action. At this point I think I am not getting the idea how it works, especially when installing the valves back... I thought you need to whack it with a hammer.

I'm telling you guys , the plunger tool is the way to go. There's zero set up time.